Resin composition for laser engraving, resin printing plate precursor for laser engraving, relief printing plate and method for production of relief printing plate

ABSTRACT

A resin composition for laser engraving comprising a binder polymer contains at least one polyester (A) selected from the group consisting of a polyester containing a hydroxycarboxylic acid unit, polycaprolactone, poly(butylene succinic acid), and derivatives thereof.

FIELD OF THE INVENTION

The present invention relates to a resin composition for laserengraving, a resin printing plate precursor for laser engraving, arelief printing plate and a method for production of a relief printingplate.

BACKGROUND OF THE INVENTION

As a method of preparation of a relief printing plate by forming aconcavity and convexity on the surface, a so-called “analog platemaking”, that is, a method in which a photosensitive elastomercomposition or photosensitive resin composition is exposed toultraviolet light through an original film to selectively cure the imagearea and the uncured area is removed with a developer is well known.

The photosensitive elastomer composition contains an elastomericpolymer, for example, a synthetic rubber, as a carrier and since therelief image formed therefrom is flexible, the printing plate isreferred to as a flexographic printing plate.

The flexographic printing plate has an aptitude for water-based ink,alcohol ink and ester ink each using ink vehicle which does not corrodethe rubber and non-solvent UV ink. Since the flexographic printing plateis flexible, it has a printing aptitude for a printing material having alarge concavity and convexity on the surface or a packaging materialhaving a low strength. However, since it is apt to be deformed by theapplication of stress, a printing pressure is necessary to be low. Onthe other hand, the photosensitive resin composition uses a plasticresin (plastic) as the carrier. The relief printing plate obtained ishard and is referred to as a resin anastatic printing plate (letterpress) which is distinguished from the flexographic printing plate.Commercially available resin anastatic printing plates include a waterdevelopment type and an alcohol development type and contain awater-soluble resin and an alcohol-soluble resin, respectively. Inkmainly used therefor is oil-based ink using ink vehicle which does notcorrode the resin and non-solvent UV ink. Since the resin anastaticprinting plate is hard, a high printing pressure can be applied andclear and sharp printing can be performed by supplying a large amount ofink.

Since the analog plate making requires an original film using a silversalt material in many cases, the time and cost for producing theoriginal film are necessary. Further, in order to develop the originalfilm, a chemical treatment is required and treatment of the waste liquidof development is also needed, the analog plate making isdisadvantageous in view of environmental health.

As a means for solving the problems according to the analog platemaking, a flexographic printing plate precursor and the resin anastaticprinting plate precursor having a laser-sensitive mask layer elementcapable of forming an image mask on site (in situ) provided on thephotosensitive elastomer layer and the photosensitive resin layer,respectively, are proposed (see, for example, Japanese Patent 2773847(corresponding to U.S. Pat. No. 5,607,814) and JP-A-9-171247 (the term“JP-A” as used herein means an “unexamined published Japanese patentapplication”) (corresponding to U.S. Pat. No. 6,020,108)). According toa plate making method of the printing plate precursor, the printingplate precursor is subjected to laser irradiation based on image datacontrolled by digital devices to form an image mask from the mask layerelement on site, then similar to the analog plate making, the printingplate precursor is exposed to ultraviolet light through the image maskand either the photosensitive elastomer layer or the photosensitiveresin layer and the image mask are removed by development. The platemaking method is referred to as a “mask CTP system” in the field offlexographic printing plate or resin anastatic printing plate. Althoughthe mask CTP system resolves the problems relating to the process ofproducing the original film described above, the problems on thetreatment of waste liquid resulting from the development of thephotosensitive elastomer layer or the photosensitive resin layer stillremain. Further, in case of the flexographic printing plate, since achlorine solvent, for example, trichloroethylene is used in thedevelopment in many instances, the system is also disadvantageous inview of working health.

As a means for solving the problems of the development process anddevelopment waste liquid, a so-called “heat development system”, thatis, a method in which the photosensitive elastomer layer is heated andthe uncured portion is removed by softening is proposed (see, forexample, JP-A-2002-357907 (corresponding to US 2003/0180655 A1)). Sincethe system does not use a developer, it is favorable in view of workingenvironment and the development waste can be subjected to incinerationdisposal without a particular segregation process. However, since thedeveloping speed of the heat development system is extremely low incomparison with that of the solvent development system, other problemsin that the working efficiency is poor and in that a complicated andcostly development apparatus is required.

As another means for solving the problems of the development process anddevelopment waste liquid, a so-called “direct engraving CTP system”,that is, a direct engraving plate making method with laser is oftenproposed. The direct engraving CTP system is literally a method ofmaking a concavity and convexity to form a relief by engraving withlaser and is advantageous in that unlike the formation of relief usingan original film, the formation of relief can be freely controlled. Forinstance, it is possible that a position where an outline character isreproduced on a printed material is deeply engraved and that in a partwhere minute halftone dots are reproduced, the halftone dots areengraved to form shoulders in order to prevent collapse of the halftonedots due to the printing pressure.

In Japanese Patent 2846954 (corresponding to U.S. Pat. No. 5,798,202),JP-A-11-338139 and JP-A-11-170718, a laser-engravable flexographicprinting plate precursor and a flexographic printing plate obtained bylaser engraving are described. In these patent documents, a monomer ismixed with an elastomeric rubber as a binder and the mixture is cured bya heat polymerization mechanism or photopolymerization mechanism andthen is subjected to laser engraving to obtain a flexographic printingplate.

As a problem of the direct engraving CTP system, it is illustrated thatthe seed of laser engraving is low. This is because in the directengraving CTP system, at least a thickness of 100 μm is necessary toengrave in view of the feature of directly forming the relief, incontrast with the mask CTP system wherein a thickness of the mask layerelement which is an object to be ablated is approximately from 1 to 10μm. Thus, some proposals intended to improve the laser engravingsensitivity have been made.

For instance, a flexographic printing plate precursor for laserengraving containing an elastomer foam is proposed (JP-A-2000-318330(corresponding to U.S. Pat. No. 6,159,659)). Although the improvement inlaser engraving sensitivity is intended by using the foam having lowdensity, a problem arises in that because of using the material of lowdensity, the strength for a printing plate is insufficient and printingdurability is severely impaired.

Also, a flexographic printing plate precursor for laser engravingincluding microspheres containing hydrocarbon gas encapsulated isproposed (US 2003/0180636 A1). The improvement in laser engravingsensitivity is intended by the system in which the gas in themicrospheres expands with heat generated by laser to destroy the gravingmaterial. However, a problem arises in that the strength for a printingplate is apt to be insufficient because of the material system includingthe gas. Further, since the gas has a property of easy expansion withheat in comparison with a solid, even when microspheres having a highheat deformation initiation temperature are used, change in the volumedue to fluctuation of the outer temperature can not be avoided and thusit is not suitable to use as a printing plate which is requiredstability of the accuracy of thickness.

Further, a flexographic printing plate precursor for laser engravingcontaining a polymer filler having a ceiling temperature of less than600K is proposed (JP-A-2000-168253 (corresponding to U.S. Pat. No.6,214,521)). Although the improvement in laser engraving sensitivity isintended by adding the polymer filler having a low depolymerizationtemperature, the use of such a polymer filler makes a concavity andconvexity on the surface of printing plate precursor which seriouslyinfluences printing quality.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a resin compositionwhich can be used in a printing plate precursor having high engravingsensitivity with laser and being capable of undergoing direct platemaking with laser engraving. Another object of the invention is toprovide a resin printing plate precursor for laser engraving having ahigh engraving sensitivity.

-   (1) A resin composition for laser engraving comprising a binder    polymer containing at least one polyester (A) selected from the    group consisting of a polyester comprising a hydroxycarboxylic acid    unit, polycaprolactone (PCL), poly(butylene succinic acid), and    derivatives thereof.-   (2) The resin composition for laser engraving as described in (1)    above, wherein the polyester (A) is selected from the group    consisting of a polyhydroxyalkanoate (PHA), a lactic acid polymer,    polyglycolic acid (PGA), polycaprolactone (PCL), poly(butylene    succinic acid), and derivatives thereof, and mixtures thereof.-   (3) The resin composition for laser engraving as described in (1)    or (2) above, wherein the polyester (A) is selected from the group    consisting of a polyhydroxyalkanoate (PHA), a lactic acid polymer,    polyglycolic acid (PGA), and derivatives thereof, and mixtures    thereof.-   (4) The resin composition for laser engraving as described in any    one of (1) to (3) above, wherein the binder polymer further contains    a hydrophilic polymer.-   (5) The resin composition for laser engraving as described in (4)    above, wherein the hydrophilic polymer is a polyvinyl alcohol (PVA)    derivative.-   (6) The resin composition for laser engraving as described in any    one of (1) to (5) above, which comprises (C) a polymerizable    compound.-   (7) The resin composition for laser engraving as described in any    one of (1) to (6) above, which comprises (D) a light-to-heat    conversion agent capable of absorbing light having a wavelength of    700 to 1,300 nm.-   (8) The resin composition for laser engraving as described in (7)    above, wherein the light-to-heat conversion agent (D) is selected    from the group consisting of carbon black, a cyanine compound and a    phthalocyanine compound.-   (9) A resin printing plate precursor for laser engraving having a    relief-forming layer comprising the resin composition for laser    engraving as described in any one of (1) to (8) above.-   (10) A method for production of a relief printing plate    comprising (1) a process of crosslinking the relief-forming layer as    described in (9) above with light and/or heat and (2) a process of    laser engraving the crosslinked relief-forming layer.-   (11) The method for production of a relief printing plate as    described in (10) above, wherein the process (1) is a process of    crosslinking the relief-forming layer with heat.-   (12) A relief printing plate produced by the method for production    of a relief printing plate as described in (10) or (11) above.-   (13) The relief printing plate as described in (12) above, wherein a    thickness of the relief-forming layer crosslinked is 0.05 mm or    more.-   (14) The relief printing plate as described in (12) or (13) above,    wherein a shore A hardness of the relief-forming layer crosslinked    is from 50 to 90°.

According to the present invention, a resin composition for laserengraving having a high engraving sensitivity to laser is obtained.Thus, the time necessary for the formation of relief can be shortened.Also, by using the resin composition for laser engraving according tothe invention, a printing plate precursor for laser engraving having thehigh engraving sensitivity can be obtained. The resin composition canalso be utilized for a resin anastatic printing plate (letter press)having a convex relief, a flexographic printing plate, a stamp, anintaglio printing plate or a screen printing plate and the applicationrange thereof should not be construed as being limited thereto.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below.

[Resin Composition for Laser Engraving]

The resin composition for laser engraving according to the inventioncomprises a binder polymer containing at least one polyester (A)selected from the group consisting of a polyester comprising ahydroxycarboxylic acid unit, polycaprolactone (PCL), poly(butylenesuccinic acid), and derivatives thereof. The term “derivative” as usedherein means a copolymer containing 50% by mole or less (preferably 30%by mole or less, more preferably 10% by mole or less) of othercopolymerization component.

The elements of the resin composition for laser engraving are describedin detail below. The resin composition for laser engraving according tothe invention is also referred to as a “resin composition according tothe invention”, hereinafter.

<(A) Polyester>

The polyester (A) for use in the invention is at least one polyesterselected from the group consisting of a polyester comprising ahydroxycarboxylic acid unit and a derivative thereof, polycaprolactone(PCL) and a derivative thereof, and poly(butylene succinic acid) and aderivative thereof. These polyesters can be used individually or incombination as the binder polymer in the resin composition according tothe invention.

The term “polyester comprising a hydroxycarboxylic acid unit” as usedherein means a polyester obtained by a polymerization reaction using ahydroxycarboxylic acid as one of the raw materials. The term“hydroxycarboxylic acid” as used herein means a compound having at leastone OH group and at least one COOH group in its molecule. It ispreferred that at least one OH group and at least one COOH group in thehydroxycarboxylic acid are located adjacent to each other and a numberof atoms connecting the OH group and the COOH group is preferably 6 orless, more preferably 4 or less.

Specifically, the polyester (A) is preferably selected from apolyhydroxyalkanoate (PHA), a lactic acid polymer, polyglycolic acid(PGA), polycaprolactone (PCL), poly(butylene succinic acid), andderivatives thereof, and mixtures thereof.

The functional mechanism according to the invention is not quite clearbut is presumed as follows.

The polyester (A) has a feature in that a part of the main chain thereofis thermally decomposed at a relatively low temperature around 300° C.at the thermal decomposition (that is, laser engraving according to theinvention) and from there, the polyester undergoes a depolymerizationreaction (a reverse reaction of a polymerization reaction in which apolymer is thermally dissociated to a low molecular monomer unit of araw material).

It is believed that the laser engraving (particularly, with anear-infrared laser) conducted in the invention is composed of fiveprocesses of (1) light absorption by a compound having an absorptionmaximum wavelength in a range of 700 to 1,300 nm, (2) light-to-heatconversion by the compound having an absorption maximum wavelength in arange of 700 to 1,300 nm, (3) heat transfer from the compound having anabsorption maximum wavelength in a range of 700 to 1,300 nm to a binderadjacent thereto, (4) thermal decomposition of the binder, and (5)dissipation of the decomposed binder.

Since the polyester (A) has the low temperature thermal decompositionproperty and depolymerization property as described above, the process(4) is accelerated by the low temperature thermal decomposition propertyand a low molecular monomer (largely volatilizes at less than 250° C.)generated by the depolymerization volatilizes immediately to progressextremely effectively the process (5). It is believed that due to thesetwo advantageous effects the laser engraving sensitivity becomesextremely high.

As an example of the polyester (A), a polyester obtained by apolymerization reaction using a hydroxycarboxylic acid as one of the rawmaterials is described below.

As PHA of the polyester (A), a polymer having a repeating monomer unitrepresented by formula (a) shown below is preferable.

In formula (a), n represents an integer of 1 to 5, R₁ represents ahydrogen atom, an alkyl group or an alkenyl group. The alkyl group andalkenyl group each preferably has from 1 to 20 carbon atoms. The polymerincludes a homopolymer wherein the combination of R₁ and n in therepeating monomer unit is same and fixed and a copolymer having at leasttwo different repeating monomer units with respect to the combination ofR₁ and n. The copolymer may be a random, block, alternative or graftpolymer. The molecular weight of PHA is ordinarily in a range from 500to 5,000,000 g/mol, preferably from 1,000 to 2,500,000 g/mol, morepreferably from 2,500 to 1,000,000 g/mol.

The PHA for use in the invention includes poly-3-hydroxybutyrate,poly-3-hydroxyvalerate, poly-3-hydroxyheptanoate,poly-3-hydroxyoctanoate, poly-4-hydroxybutyrate,poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate),poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) and other copolymers. Thecopolymer of PHA contains ordinarily 40% or more and less than 100%,preferably from 60 to 98%, of 3-hydroxybutyrate monomer.

Further, as the polyester (A), a copolymer can also be used wherein as acomonomer copolymerizable with the repeating monomer unit represented byformula (a), a monomer used in a polyester which can be used togetherwith the polyester (A) described hereinafter is used.

The lactic acid polymer for use in the invention includes polylacticacid (in formula (a), R₁ represents a methyl group and n represents 0)and a copolymer of lactic acid and a hydroxycarboxylic acid. Examples ofthe hydroxycarboxylic acid include glycolic acid (in formula (a), R₁represents a hydrogen atom and n represents 0), hydroxybutyric acid,hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid andhydroxyheptanoic acid. Preferable molecular structure of the polylacticacid is composed of from 85 to 100% of unit of any one of L-lactic acidand D-lactic acid and 0 to 15% of lactic acid unit of the antipode. Thecopolymer of lactic acid and a hydroxycarboxylic acid is composed offrom 85 to less than 100% of unit of any one of L-lactic acid andD-lactic acid and more than 0 to 15% of a hydroxycarboxylic acid unit.From the standpoint of availability of the raw materials, DL-lactic acid(racemic body) may be used as the lactic acid. Preferable examples ofthe hydroxycarboxylic acid include glycolic acid and hydroxycaproicacid.

The lactic acid polymer can be obtained by selecting as a raw materialmonomer, a monomer having the desired structure from L-lactic acid,D-lactic acid and a hydroxycarboxylic acid and conducting dehydrationpolycondensation. Preferably, it can be obtained by selecting a monomerhaving the desired structure from lactide of a cyclic dimer of lacticacid, glycolide of a cyclic dimer of glycolic acid and a lactone andconducting a ring-opening polymerization. The lactide includes L-lactideof a cyclic dimer of L-lactic acid, D-lactide of a cyclic dimer ofD-lactic acid, meso-lactide of a cyclic dimer of D-lactic acid andL-lactic acid and a DL-lactide of a racemic mixture of D-lactide andL-lactide. Any lactide may be used in the invention. However, as themain raw material, D-lactide, L-lactide, glycolide or caprolactone ispreferably used.

As to the polylactic acid and copolymer of lactic acid and glycolicacid, a lactic acid/glycolic acid ratio (molar ratio) is preferably from100/0 to 30/70, more preferably from 100/0 to 40/60, and aweight-average molecular weight is preferably approximately from 1,000to 100,000, more preferably approximately from 2,000 to 80,000.

Of the polylactic acid and copolymer of lactic acid and glycolic acid,the polylactic acid is preferable than the copolymer of lactic acid andglycolic acid in view of maintaining strong film property.

The polycaprolactone (PCL) (in formula (a), R₁ represents a hydrogenatom and n represents 4) used as the polyester (A) may be a homopolymeror a copolymer of caprolactone and other lactone and includes thepolyesters having the same structure represented by formula (a) above.

The poly(butylene succinic acid) used as the polyester (A) is not apolyester composed of only a hydroxycarboxylic acid unit but a polymersynthesized from 1,4-butanediol and succinic acid and ahydroxycarboxylic acid may be used together.

As the polyesters described for the polyester (A), copolymers can alsobe used wherein as a copolymerizable comonomer, a monomer used in apolyester which can be used together with the polyester (A) describedhereinafter is used.

Examples of polyester other than the polyester (A) preferably usedtogether with the polyester (A) are described below. However,poly(butylene succinic acid) is used as the polyester (A).

Such other polyesters include a polyester composed of an aliphatic(including cyclic aliphatic) glycol, an aromatic dicarboxylic acid or anacid anhydride thereof, an aliphatic dicarboxylic acid or an acidanhydride thereof (hereinafter also simply referred to as an “aliphaticdicarboxylic acid”), as a monomer, for the purpose, for example, ofadjusting water-resistance and flexibility of a film.

If desired, the other polyester may include as the third component, atleast one polyfunctional component selected from a tri-functional ortetra-functional polyhydric alcohol and a polyvalent carboxylic acid oran acid hydride thereof.

As the glycol, ethylene glycol, 1,4-butanediol, 1,6-hexanediol,1,8-octanediol, 1,10-decanediol, 1,4-cyclohexanediol and mixturesthereof are preferably used, but the glycol should not be construed asbeing limited thereto.

As the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid,phthalic acid, naphthalenedicarboxylic acid and mixtures thereof arepreferably used, but the aromatic dicarboxylic acid should not beconstrued as being limited thereto.

As the aliphatic dicarboxylic acid, succinic acid, adipic acid, subericacid, sebacic asid, 1,10-decanedicarboxylic acid, succinic anhydride,1,4-cyclohexanedicarboxylic acid and mixtures thereof are preferablyused, but the aliphatic dicarboxylic acid should not be construed asbeing limited thereto.

As the best mode according to the invention, the lactic acid polymer ispreferable and polylactic acid and polyglycolic acid are more preferablefrom the standpoint of high engraving sensitivity.

The content of the polyester (A) in the resin composition according tothe invention is preferably from 5 to 95% by weight, more preferablyfrom 15 to 85% by weight, particularly preferably from 25 to 70% byweight, in view of well maintaining the film property and engravingsensitivity.

In the resin composition according to the invention, (B) a binderpolymer used together with the polyester (A) can be used as the binderpolymer other than the polyester capable of being used togetherdescribed above. The polyester other than the polyester (A) is also thebinder polymer (B).

<(B) Binder Polymer>

The binder polymer (B) includes a polymer containing a carbon-carbonunsaturated bond in at least any one of its main chain and side chain.Hereinafter, the binder polymer (B) is also referred to as “Binder (B)”.As the binder (B), among the polyester compounds illustrated below, thathaving the same structure as the polyester (A) is omitted.

The polymer containing a carbon-carbon unsaturated bond in its mainchain includes, for example, SB (polystyrene-polybutadiene), SBS(polystyrene-polybutadiene-polystyrene), SIS(polystyrene-polyisoprene-polystyrene) and SEBS(polystyrene-polyethylene/polybutylene-polystyrene).

When a polymer containing a polymerizable unsaturated group having ahigh reactivity, for example, a methacryloyl group, is used as thepolymer having a carbon-carbon unsaturated bond in its side chain, afilm having an extremely high mechanical strength can be prepared. Inparticular, as for a polyurethane-series or polyester-seriesthermoplastic elastomer, it is possible to introduce relatively easilythe polymerizable unsaturated group having a high reactivity into itsmolecule. The terminology “to introduce into its molecule” as usedherein means and includes cases wherein the polymerizable unsaturatedgroup is bonded at either both terminals or one terminal of the polymermain chain, at a terminal of the polymer side chain, or directly to thepolymer main chain or side chain. Specifically, for instance, thepolymer having the polymerizable unsaturated group directly introducedat the terminal of the molecule thereof may be used. Alternatively,other method, for example, a method is preferably employed in which acompound having a molecular weight of about several thousands andincluding plural reactive groups, for example, a hydroxy group, an aminogroup, an epoxy group, a carboxyl group, an acid anhydride group, aketone group, a hydrazine residue, an isocyanate group, anisothiocyanate group, a cyclic carbonate group or an ester group isreacted with a connecting agent having plural groups capable ofconnecting with the above-described reactive group (for example, apolyisocyanate group reacting with the hydroxy group or amino group) toconduct the adjustment of molecular weight and conversion to a terminalbonding group and then the resulting compound is reacted with an organiccompound having a group capable of reacting with the terminal connectinggroup and a polymerizable unsaturated group to introduce thepolymerizable unsaturated group into the terminal.

The binder (B) may be a polymer not having a carbon-carbon unsaturatedbond may be used as well as the above-described polymer having acarbon-carbon unsaturated bond. The polymer not having a carbon-carbonunsaturated bond includes, for example, a resin easily prepared byadding hydrogen to the olefin portion of the above-described polymerhaving a carbon-carbon unsaturated bond or a resin easily prepared bypolymerization using a raw material previously added hydrogen to itsolefin portion (for example, a compound which is obtained byhydrogenation of butadiene, isoprene or the like).

The binder (B) may be an elastomer or a non-elastomer.

The number average molecular weight of the binder polymer is preferablyin a range of 1,000 to 1,000,000, more preferably in a range of 5,000 to500,000. When the number average molecular weight thereof is in therange of 1,000 to 1,000,000, the mechanical strength of the film formedcan be ensured. The term “number average molecular weigh” as used hereinmeans a molecular weight obtained by measuring using gel permeationchromatography (GPC) and calculating in terms of standard polystyrene ofa known molecular weight.

In the case where the polymer not having a carbon-carbon unsaturatedbond is used together with the polymer having a carbon-carbonunsaturated bond, the polymer not having a carbon-carbon unsaturatedbond is ordinarily used from 1 to 90% by weight, preferably from 5 to80% by weight, to the polymer having a carbon-carbon unsaturated bond.In the invention, only the polymer not having a carbon-carbonunsaturated bond may be used as the binder (B).

As the binder (B), a resin easily liquefiable or a resin easilydecomposable is preferable. The resin easily decomposable preferablycontains in the molecular chain as a monomer unit easily decomposable,for example, a monomer unit derived from styrene, a-methylstyrene,a-methoxystyrene, an acryl ester, a methacryl ester, an ester compoundother than those described above, an ether compound, a nitro compound, acarbonate compound, a carbamoyl compound, a hemiacetal ester compound,an oxyethylene compound or an aliphatic cyclic compound. In particular,a polyether, for example, polyethylene glycol, polypropylene glycol orpolytetraethylene glycol, an aliphatic polycarbonate, an aliphaticpolycarbamate, polymethyl methacrylate, polystyrene, nitrocellulose,polyoxyethylene, polynorbornene, hydrogenated polycyclohexadiene or apolymer having a molecular structure of many branched structures, forexample, a dendrimer is the representative example of the resin easilydecomposable. Also, a polymer containing a lot of oxygen atoms in itsmolecular chain is preferable from the standpoint of thedecomposability. Among them, the compound having a carbonate group, acarbamate group or a methacryl group in the polymer main chain ispreferable in view of the high heat decomposability. For instance, apolyester or polyurethane synthesized using as the raw material,(poly)carbonatediol or (poly)carbonate dicarboxylic acid or a polyamidesynthesized using as the raw material, (poly)carbonate diamine isillustrated as a preferable example of the polymer of good heatdecomposability. The polymer may contain a polymerizable unsaturatedgroup in the main chain or side chain thereof. In particular, when thepolymer has a reactive functional group, for example, a hydroxy group,an amino group or a carboxyl group, it is easy to introduce thepolymerizable unsaturated group.

The thermoplastic elastomer is not particularly restricted and includes,for example, a urethane-series thermoplastic elastomer, an ester-seriesthermoplastic elastomer, an amide-series thermoplastic elastomer or asilicone-series thermoplastic elastomer. In order to more increase theheat decomposability, a polymer wherein an easily decomposablefunctional group, for example, a carbamoyl group or a carbonate group isintroduced into its main chain can be used. Also, it may be used as amixture with a polymer of higher heat decomposability. Since thethermoplastic elastomer is fluidized by heating, it is possible to bewell mixed. The term “thermoplastic elastomer” as used herein means amaterial which exhibits rubber elasticity at ambient temperature and isfluidized by heating to undergo fabrication as an ordinary thermoplasticplastic. With respect to the molecular structure, the thermoplasticelastomer comprises a soft segment like a polyether or a rubber moleculeand a hard segment which prevents plastic deformation around ambienttemperature as vulcanized rubber. As the hard segment, various types,for example, a frozen phase, a crystalline phase, a hydrogen bond or anionic crosslinkage are present.

The kind of thermoplastic elastomer can be selected depending on the useof the resin composition. For instance, in the field requiring solventresistance, a urethane-series, ester-series, amide-series orfluorine-series thermoplastic elastomer is preferable and in the fieldrequiring heat resistance, a urethane-series, olefin-series,ester-series or fluorine-series thermoplastic elastomer is preferable.Further, the hardness can be widely changed depending on the kind ofthermoplastic elastomer.

The non-elastomeric thermoplastic resin is not particularly restrictedand includes, for example, a polyester resin, an unsaturated polyesterresin, a polyamide resin, a polyamideimide resin, a polyurethane resin,an unsaturated polyurethane resin, a polysulfone resin, apolyethersulfone resin, a polyimide resin, a polycarbonate resin, a fullaromatic polyester resin and a hydrophilic polymer containing ahydroxyethylene unit (for example, a polyvinyl alcohol derivative).

As the binder (B), a hydrophilic polymer is preferable.

<Hydrophilic Polymer>

The term “hydrophilic polymer” as used herein means a polymer which issoluble or swellable in water. Hydrophilic resins broadly haveresistance to oil-based ink and are preferably used. Examples of such ahydrophilic resin include a hydrophilic polymer containinghydroxyethylene, a polysaccharide having a hydrophilic functional groupincluding cellulose, an acrylic resin containing a salt structure formedby neutralization of an acidic functional group, for example, sodiumpolyacrylate or a salt structure formed by neutralization of an aminogroup or an onium structure, a polyamide resin or polyester resin havingincorporated thereto a hydrophilic group, for example, polyethyleneoxide, and gelatin.

In view of exhibiting good hydrophilicity, a hydrophilic polymercontaining hydroxyethylene, a cellulose containing a polar group, forexample, an amino group, a carboxylic acid group, a sulfonic acid groupor a sulfuric acid group or a salt structure formed by neutralization ofeach of these groups, an acrylic resin containing a polar group, forexample, an amino group, a carboxylic acid group, a sulfonic acid groupor a sulfuric acid group or a salt structure formed by neutralization ofeach of these groups, or a polyamide resin is preferable.

A hydrophilic polymer containing hydroxyethylene, an acrylic resincontaining a polar group, for example, an amino group, a carboxylic acidgroup, a sulfonic acid group or a sulfuric acid group or a saltstructure formed by neutralization of each of these groups, or apolyamide resin is more preferable, and a polyvinyl alcohol or apolyamide resin is particularly preferable. Especially, a polyvinylalcohol derivative is preferable.

A PVA derivative is preferable as the hydrophilic polymer. The PVAderivative used in the invention means a polymer, copolymer or amodified product thereof containing a hydroxyethylene unit from 0.1 to100% by mole, preferably from 1 to 98% by mole, more preferably from 5to 95% by mole. Specifically, polyvinyl alcohol per se is also included.A monomer for forming the copolymer can be appropriately selected fromknown copolymerizable monomers. The modified product includes thosedescribed below.

As the PVA derivative, polyvinyl alcohol and a vinyl alcohol/vinylacetate copolymer (partially saponified polyvinyl alcohol) areparticularly preferably exemplified and the modified products thereofare also particularly preferable.

As the hydrophilic polymer, an individual polymer may be used or pluralkinds of polymers may be used as a mixture.

As the hydrophilic polymer, it is particularly preferred to use the PVAderivative together with a hydrophilic polymer not containing ahydroxyethylene unit. The hydrophilic polymer not containing ahydroxyethylene unit is also referred to as a “non-PVA derivative”.

The non-PVA derivative means a hydrophilic polymer which has polaritysimilar to the PVA derivative so as to exhibit compatibility with thePVA derivative. A polyamide obtained by polymerization of adipic acidand 1,6-hexanediamine or polymerization of only ε-caprolactam iswater-insoluble and has the polarity different from that of the PVAderivative. A polyamide prepared by introducing a hydrophilic group, forexample, polyethylene glycol or piperazine into such a water-insolublepolyamide is preferably used as the non-PVA derivative because thepolyamide exhibits compatibility with the PVA derivative due to thefunction of the hydrophilic group introduced. Specifically, since thehydrophilic polyamide used as the non-PVA derivative has thecompatibility with the PVA derivative, it can easily penetrate betweenmolecules of the PVA derivative and the intermolecular force between themolecules of PVA derivative and non-PVA derivative is reduced resultingin imparting flexibility to the polymer.

A polyamide having a polyethylene glycol unit is obtained by undergoinga reaction of ε-caprolactam and/or adipic acid with polyethylene glycolin which both terminals are modified with amines and a hydrophilicpolyamide having a piperazine skeleton by undergoing a reaction ofε-caprolactam and/or adipic acid with piperazine. Also, a hydrophilicpolyamide having a crosslinkable functional group introduced is obtainedby undergoing reaction of an amido group in a hydrophilic polyamide withan epoxy group of glycidyl methacrylate. The non-PVA derivatives may beused individually or as a mixture of two or more thereof.

Examples of the modified product of PVA derivative include a polymerobtained by modifying at least a part of hydroxy groups ofhydroxyethylene units to carboxy groups, a polymer obtained by modifyingat least a part of hydroxy groups of hydroxyethylene monomer units to(meth)acryloyl groups, a polymer obtained by modifying at least a partof hydroxy groups of hydroxyethylene monomer units to amino groups and apolymer obtained by introducing ethylene glycol, propylene glycol ordimers thereof into at least a part of hydroxy groups of hydroxyethylenemonomer units.

The polymer obtained by modifying at least a part of the hydroxy groupsto carboxy groups can be obtained by esterification of polyvinyl alcoholor partially saponified polyvinyl alcohol with a polyfunctionalcarboxylic acid, for example, succinic acid, maleic acid or adipic acid.The amount of carboxy group introduced is preferably from 0.01 to 1.00mol, more preferably from 0.05 to 0.80 mol, per mol of the hydroxygroup.

The polymer obtained by modifying at least a part of the hydroxy groupsto (meth)acryloyl groups can be obtained by addition of a glycidyl(meth)acrylate to the above-described carboxyl group-modified polymer orby esterification of polyvinyl alcohol or partially saponified polyvinylalcohol with (meth)acrylic acid. The amount of (meth)acryloyl groupintroduced is preferably from 0.01 to 1.00 mol, more preferably from0.03 to 0.50 mol, per mol of the hydroxy group. The expression of“(meth)acryloyl group” is used as the collective term for an acryloylgroup and a methacryloyl group. The expression of “(meth)acrylate” isused as the collective term for an acrylate and a methacrylate. Theexpression of “(meth)acrylic acid” is used as the collective term foracrylic acid and methacrylic acid.

The polymer obtained by modifying at least a part of hydroxy groups aremodified to amino groups can be obtained by esterification of polyvinylalcohol or partially saponified polyvinyl alcohol with a carboxylic acidcontaining an amino group, for example, carbamic acid. The amount ofamino group introduced is preferably from 0.01 to 1.00 mol, morepreferably from 0.05 to 0.70 mol, per mol of the hydroxy group.

The polymer obtained by introducing ethylene glycol, propylene glycol ordimers thereof introduced into at least a part of the hydroxy groups canbe obtained by heating polyvinyl alcohol or partially saponifiedpolyvinyl alcohol together with a glycol in the presence of a sulfuricacid catalyst and removing water as a byproduct from the reactionsystem. The total amount of ethylene glycol, propylene glycol and dimersthereof introduced is preferably from 0.01 to 0.90 mol, more preferablyfrom 0.03 to 0.50 mol, per mol of the hydroxy group.

Among the modified products of PVA derivative, the polymer obtained bymodifying at least a part of the hydroxy groups to (meth)acryloyl groupsis particularly preferably used. The reason for this is that the directintroduction of unreacted crosslinkable functional group into thehydrophilic polymer makes it possible, for example, to increase strengthof the relief-forming layer without using a large amount ofpolyfunctional monomers as the ethylenically unsaturated monomerdescribed with respect to the polymerizable monomer (C) hereinafter sothat good compatibility between the flexibility and the strength of therelief-forming layer can be achieved.

The weight average molecular weight (measured by GPC and calculated interms of polystyrene) of the hydrophilic polymer is preferably from5,000 to 500,000. When the weight average molecular weight thereof is5,000 or more, the polymer is excellent in the configuration retentionproperty as a carrier resin. When the weight average molecular weightthereof is 500,000 or less, the polymer is easily soluble in a solvent,for example, water and advantageous to the preparation of resincomposition for laser engraving. The weight average molecular weightthereof is more preferably from 10,000 to 400,000, particularlypreferably from 15,000 to 300,000.

The content of the hydrophilic polymer in the resin composition forlaser engraving is preferably from 15 to 79% by weight, more preferablyfrom 30 to 65% by weight, based on the total solid content of the resincomposition. When the content of the hydrophilic polymer is regulated to15% by weight or more, the printing durability sufficient for using asthe relief printing plate is obtained. When the content of thehydrophilic polymer is regulated to 79% by weight or less, theflexibility sufficient for using as the relief printing plate isobtained without accompanying the lack of other components.

The total content of the PVA derivative and non-PVA derivative when usedtogether in the resin composition for laser engraving is preferably from30 to 80% by weight, more preferably from 40 to 70% by weight, based onthe total solid content of the resin composition. This is because whenthe total content of the PVA derivative and non-PVA derivative isregulated to 30% by weight or more, it is possible to prevent cold flowof the printing plate precursor, whereas when the total content of thePVA derivative and non-PVA derivative is regulated to 80% by weight orless, the printing durability sufficient for using as the reliefprinting plate is obtained without accompanying the lack of othercomponents.

In the case of using the PVA derivative together with the non-PVAderivative in the resin composition for laser engraving, the content ofthe PVA derivative is preferably from 15 to 79% by weight, morepreferably from 30 to 65% by weight, based on the total solid content ofthe resin composition. When the content of the PVA derivative isregulated to 15% by weight or more, the printing durability sufficientfor using as the relief printing plate is obtained. When the content ofthe PVA derivative is regulated to 79% by weight or less, theflexibility sufficient for using as the relief printing plate isobtained without accompanying the lack of other components. On the otherhand, the content of the non-PVA derivative is preferably from 1 to 15%by weight, more preferably from 3 to 10% by weight, based on the totalsolid content of the resin composition. When the content of the non-PVAderivative is regulated to 1% by weight or more, flexibilization of thePVA derivative is efficiently performed so that the flexibilitysufficient for using as the relief printing plate is obtained and due tothe strong characteristic of the non-PVA derivative, printing durabilitysufficient for using as the relief printing plate is also obtained. Whenthe content of the non-PVA derivative is regulated to 15% by weight orless, the amount of tacky engraving scrap resulting from the non-PVAderivative is reduced.

According to the invention, although it is possible to use, togetherwith the component (A), the PVA derivative alone or to use the PVAderivative together with the non-PVA derivative, it is preferable to usethe PVA derivative together with the non-PVA derivative from the standpoint of ensuring aptitudes necessary for the flexographic printing, forexample, flexibility or abrasion resistance of film. In case of usingthe PVA derivative together with the non-PVA derivative, both of the PVAderivative and the non-PVA derivative may be used individually, eitherof them may be used plurally or both of them are used plurally.

If the hydrophilic polymer is used, the engraving scrap is hydrophilicand as a result, the engraving scrap can be removed by only a simpleoperation of washing with tap water after the engraving. When ahydrophobic polymer or elastomer, for example, SB(polystyrene-polybutadiene), SBS(polystyrene-polybutadiene-polystyrene), SIS(polystyrene-polyisoprene-polystyrene) or SEBS(polystyrene-polyethylene/polybutylene-polystyrene), a polyurethane oran acrylic resin is used as the main component of binder, cases wherethe removal of engraving scrap by washing with water is difficult mayoccur because the engraving scrap is hydrophobic.

Also, it is preferred that when, for example, the PVA derivative is usedas the hydrophilic polymer (particularly, non-elastomer having a glasstransition temperature of room temperature or higher) according thefeature of the invention, the melting in the edge of relief at theengraving resulting from the low glass transition temperature tends tobe prevented in comparison with the case of using the above-describedhydrophobic polymer or elastomer (mostly having a glass transitiontemperature of room temperature or lower).

A relatively hydrophobic binder polymer as mentioned above may be usedtogether the hydrophilic polymer. As the relatively hydrophobic binderpolymer, a polymer containing a monomer described below as apolymerization component or copolymerization component is used in orderto adjust properties, for example, hardness or flexibility of a film atthe preparation and compatibility with other component, for example, apolymerizable compound or an initiator.

Specifically, a (meth)acrylate having a hydroxy group, for example,2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, 3-chloro-2-hydroxypropyl(meth)acrylate orβ-hydroxy-β′-(meth)acryloyloxyethyl phthalate, an alkyl(meth)acrylate,for example, methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, butyl(meth)acrylate, isoamyl(meth)acrylate,2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate orstearyl(meth)acrylate, a cycloalkyl(meth)acrylate, for example,cyclohexyl(meth)acrylate, a halogenated alkyl(meth)acrylate, forexample, chloroethyl(meth)acrylate or chloropropyl(meth)acrylate, analkoxyalkyl(meth)acrylate, for example, methoxyethyl(meth)acrylate,ethoxyethyl(meth)acrylate or butoxyethyl(meth)acrylate, aphenoxyalkyl(meth)acrylate, for example, phenoxyethyl acrylate ornonylphenoxyethyl(meth)acrylate, an alkoxyalkylene glycol(meth)acrylate,for example, ethoxydiethylene glycol(meth)acrylate, methoxytriethyleneglycol(meth)acrylate or methoxydipropylene glycol(meth)acrylate, a(meth)acrylamide, for example, (meth)acrylamide,diacetone(meth)acrylamide or N,N′-methylenebis(meth)acrylamide, acompound having only one ethylenically unsaturated bond, for example,2,2-dimethylaminoethyl(meth)acrylate,2,2-diethylaminoethyl(meth)acrylate,N,N-dimethylaminoethyl(meth)acrylamide orN,N-dimethylaminopropyl(meth)acrylamide, and a compound having two ormore ethylenically unsaturated bonds, for instance, a polyethyleneglycol di(meth)acrylate, for example, diethylene glycoldi(meth)acrylate, a polypropylene glycol di(meth)acrylate, for example,dipropylene glycol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, glycerol tri(meth)acrylate, a polyvalent(meth)acrylate obtained by an addition reaction of ethylene glycoldiglycidyl ether with a compound having an ethylenically unsaturatedbond and an active hydrogen atom, for example, an unsaturated carboxylicacid or unsaturated alcohol, a polyvalent(meth)acrylate obtained by anaddition reaction of an unsaturated epoxy compound, for example,glycidyl (meth)acrylate with a compound having an active hydrogen atom,for example, an carboxylic acid or amine, a polyvalent(meth)acrylamide,for example, methylenebis(meth)acrylamide, or a polyvalent vinylcompound, for example, divinylbenzene are exemplified. The monomers maybe used individually or in combination of two or more thereof in theinvention.

As the monomer for the polymerization component,2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,2-hydroxybutyl(meth)acrylate, an alkoxyalkylene glycol(meth)acrylate,for example, ethoxydiethylene glycol(meth)acrylate, methoxytriethyleneglycol(meth) acrylate or methoxydipropylene glycol(meth)acrylate,(meth)acrylamide, diacetone(meth)acrylamide, cyclohexyl(meth)acrylate,benzyl(meth)acrylate and N-acryloylmorpholine are preferable in view ofa film-forming property. Among them, the acrylate is particularlypreferable from the standpoint of ensuring flexibility of the polymerobtained.

Further, the polymer witch may be used together includes the following.

Specifically, a polymer containing any one of an olefin bond and acarbon-carbon triple bond in its main chain is exemplified. Examplesthereof include SB (polystyrene-polybutadiene), SBS(polystyrene-polybutadiene-polystyrene), SIS(polystyrene-polyisoprene-polystyrene) and SEBS(polystyrene-polyethylene/polybutylene-polystyrene).

The binder polymer which may be used together with the hydrophilicpolymer is preferably used in an amount for increasing the film propertywithout accompanying decrease in the engraving sensitivity. The contentthereof is preferably from 1 to 50% by weight, more preferably from 1 to30% by weight, most preferably from 1 to 10% by weight, based on thetotal binder polymer.

In view of engraving sensitivity, a rate of the polyester (A) and thebinder (B) used is preferably from 0.1:99.9 to 99.9:0.1, more preferablyfrom 5:95 to 80:20, particularly preferably from 10:90 to 50:50, interms of a ratio of (A): (B) taking the total amount of (A) and (B) 100.

The polyester (A) may be incorporated into the resin composition in anystate of homogeneous form, particulate form and fibrous form to form afilm and from the stand point of well maintaining hardness of the filmand abrasion resistance, it is preferred to form the film in thehomogeneous form or particulate form.

In case of using the polyester (A) together with the bonder (B) which isa hydrophilic polymer, it is preferred to mix the polyester (A) with thebinder (B) in the sate of an emulsion (also referred to as a suspensionor a latex), because a solvent for preparing the composition is mainlywater or an alcohol. Preferable examples of the polylactic acid emulsioninclude Landy PL series (produced by Miyoshi Oil and Fat Co., Ltd.) andBionole (produced by Showa Highpolymer Co., Ltd.).

In case of using the polyester (A) in the state of an emulsion, asurfactant or a stabilizer for assisting dispersion of the polyester (A)may be added in order to prevent aggregation and precipitation of thepolyester (A) during preparation or drying of the composition.

The resin composition according to the invention preferably contains (C)a polymerizable compound, (D) a light-to-heat conversion agent, (E) apolymerization initiator and (F) a plasticizer. These components aredescribed in detail below.

<(C) Polymerizable Compound>

The polymerizable compound (C) according to the invention means acompound having at least one carbon-carbon unsaturated bond capable ofundergoing a radical polymerization triggered by the generation of aninitiation radical derived from the polymerization initiator.

The polymerizable compound (C) is described in greater detail belowtaking a case wherein an addition polymerizable compound is used as anexample.

The polymerizable compound preferably used in the invention includes anaddition-polymerizable compound having at least one ethylenicallyunsaturated double bond. The addition-polymerizable compound ispreferably selected from compounds having at least one, preferably twoor more, terminal ethylenically unsaturated double bonds. Such compoundsare widely known in the field of art and they can be used in theinvention without any particular limitation. The compound has a chemicalform, for example, a monomer, a prepolymer, specifically, a dimer, atrimer or an oligomer, or a copolymer thereof, or a mixture thereof.Examples of the monomer include unsaturated carboxylic acids (forexample, acrylic acid, methacrylic acid, itaconic acid, crotonic acid,isocrotonic acid or maleic acid) and esters or amides thereof.Preferably, esters of an unsaturated carboxylic acid with an aliphaticpolyhydric alcohol compound and amides of an unsaturated carboxylic acidwith an aliphatic polyvalent amine compound are used. An additionreaction product of an unsaturated carboxylic acid ester or amide havinga nucleophilic substituent, for example, a hydroxy group, an amino groupor a mercapto group, with a monofunctional or polyfunctional isocyanateor epoxy, or a dehydration condensation reaction product of theunsaturated carboxylic acid ester or amide with a monofunctional orpolyfunctional carboxylic acid is also preferably used. Furthermore, anaddition reaction product of an unsaturated carboxylic acid ester oramide having an electrophilic substituent, for example, an isocyanatogroup or an epoxy group with a monofunctional or polyfunctional alcohol,amine or thiol, or a substitution reaction product of an unsaturatedcarboxylic acid ester or amide having a releasable substituent, forexample, a halogen atom or a tosyloxy group with a monofunctional orpolyfunctional alcohol, amine or thiol is also preferably used. Inaddition, compounds in which the unsaturated carboxylic acid describedabove is replaced by an unsaturated phosphonic acid, styrene, vinylether or the like can also be used.

With respect to specific examples of the monomer, which is an ester ofan aliphatic polyhydric alcohol compound with an unsaturated carboxylicacid, as an acrylic acid ester, for example, ethylene glycol diacrylate,triethylene glycol diacrylate, 1,3-butanediol diacrylate, tetramethyleneglycol diacrylate, propylene glycol diacrylate, neopentyl glycoldiacrylate, trimethylolpropane triacrylate, trimethylolpropanetri(acryloyloxypropyl)ether, trimethylolethane triacrylate, hexanedioldiacrylate, 1,4-cyclohexanediol diacrylate, tetraethylene glycoldiacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate, dipentaerythritol diacrylate,dipentaerythritol hexaacrylate, sorbitol triacrylate, sorbitoltetraacrylate, sorbitol pentaacrylate, sorbitol hexaacrylate,tri(acryloyloxyethyl)isocyanurate and polyester acrylate oligomer arerecited.

As a methacrylic acid ester, for example, tetramethylene glycoldimethacrylate, triethylene glycol dimethacrylate, neopentyl glycoldimethacrylate, trimethylolpropane trimethacrylate, trimethylolethanetrimethacrylate, ethylene glycol dimethacrylate, 1,3-butanedioldimethacrylate, hexanediol dimethacrylate, pentaerythritoldimethacrylate, pentaerythritol trimethacrylate, pentaerythritoltetramethacrylate, dipentaerythritol dimethacrylate, dipentaerythritolhexamethacrylate, sorbitol trimethacrylate, sorbitol tetramethacrylate,bis[p-(3-methacryloxy-2-hydroxypropoxy)phenyl]dimethylmethane andbis[p-(methacryloxyethoxy)phenyl]dimethylmethane are recited.

As an itaconic acid ester, for example, ethylene glycol diitaconate,propylene glycol diitaconate, 1,3-butanediol diitaconate, 1,4-butanedioldiitaconate, tetramethylene glycol diitaconate, pentaerythritoldiitaconate and sorbitol tetraitaconate are recited.

As a crotonic acid ester, for example, ethylene glycol dicrotonate,tetramethylene glycol dicrotonate, pentaerythritol dicrotonate andsorbitol tetracrotonate are recited.

As an isocrotonic acid ester, for example, ethylene glycoldiisocrotonate, pentaerythritol diisocrotonate and sorbitoltetraisocrotonate are recited.

As a maleic acid ester, for example, ethylene glycol dimaleate,triethylene glycol dimaleate, pentaerythritol dimaleate and sorbitoltetramaleate are recited.

Other examples of the ester, which can be preferably used, includealiphatic alcohol esters described in JP-B-46-27926, JP-B-51-47334 andJP-A-57-196231, esters having an aromatic skeleton described inJP-A-59-5240, JP-A-59-5241 and JP-A-2-226149, and esters containing anamino group described in JP-A-1-165613.

The above-described ester monomers can also be used as a mixture.

Specific examples of the monomer, which is an amide of an aliphaticpolyvalent amine compound with an unsaturated carboxylic acid, includemethylene bisacrylamide, methylene bismethacrylamide, 1,6-hexamethylenebisacrylamide, 1,6-hexamethylene bismethacrylamide, diethylenetriaminetrisacrylamide, xylylene bisacrylamide and xylylene bismethacrylamide.

Other preferable examples of the amide monomer include amides having acyclohexylene structure described in JP-B-54-21726.

Urethane type addition polymerizable compounds produced using anaddition reaction between an isocyanate and a hydroxy group are alsopreferably used, and specific examples thereof include vinylurethanecompounds having two or more polymerizable vinyl groups per moleculeobtained by adding a vinyl monomer containing a hydroxy grouprepresented by formula (V) shown below to a polyisocyanate compoundhaving two or more isocyanate groups per molecule, described inJP-B-48-41708.

CH₂═C(R)COOCH₂CH(R′)OH   (V)

wherein R and R′ each independently represents H or CH₃.

Also, urethane acrylates described in JP-A-51-37193, JP-B-2-32293 andJP-B-2-16765, and urethane compounds having an ethylene oxide skeletondescribed in JP-B-58-49860, JP-B-56-17654, JP-B-62-39417 andJP-B-62-39418 are preferably used.

Furthermore, the resin composition capable of being cured at short timescan be obtained by using an addition polymerizable compound having anamino structure or a sulfide structure in its molecule described inJP-A-63-277653, JP-A-63-260909 and JP-A-1-105238.

Other examples include polyfunctional acrylates and methacrylates, forexample, polyester acrylates and epoxy acrylates obtained by reacting anepoxy resin with acrylic acid or methacrylic acid described inJP-A-48-64183, JP-B-49-43191 and JP-B-52-30490. Specific unsaturatedcompounds described in JP-B-46-43946, JP-B-1-40337 and JP-B-1-40336, andvinylphosphonic acid series compounds described in JP-A-2-25493 can alsobe exemplified. In some cases, structure containing a perfluoroalkylgroup described in JP-A-61-22048 can be preferably used. Moreover,photocurable monomers or oligomers described in Nippon SecchakuKyokaishi (Journal of Japan Adhesion Society), Vol. 20, No. 7, pages 300to 308 (1984) can also be used.

In view of the photo-speed, a structure having a large content ofunsaturated groups per molecule is preferred and in many cases, adifunctional or more functional compound is preferred. In order toincrease the strength of image area, that is, cured layer, atrifunctional or more functional compound is preferred. A combinationuse of compounds different in the functional number or in the kind ofpolymerizable group (for example, an acrylic acid ester, a methacrylicacid ester, a styrene compound or a vinyl ether compound) is aneffective method for controlling both the sensitivity and the strength.The polymerizable compound is preferably used in an amount from 10 to60% by weight, more preferably from 15 to 40% by weight, based on thenonvolatile component in the resin composition. The polymerizablecompounds may be used individually or in combination of two or morethereof. By using the polymerizable compound, the film physicalproperty, for example, brittleness or flexibility can also be adjusted.

Before and/or after the laser decomposition, the resin composition forlaser engraving containing the polymerizable compound can be polymerizedand cured with energy, for example, light or heat.

Preferable specific examples of the polymerizable compound for use inthe resin composition for laser engraving according to the invention areset forth below.

Of the polymerizable compounds used in the invention, a polymerizablecompound containing a sulfur (S) atom is particularly preferred from thestandpoint that melting in the edge of relief hardly occurs and a sharprelief is easily obtained. Specifically, it is preferred to contain Satom in the crosslinked network.

Although the polymerizable compound containing S atom may be usedtogether with the polymerizable compound not containing S atom, it ispreferred to use the polymerizable compound containing S atom alone fromthe standpoint that the melting in the edge of relief hardly occurs.Further, it is also possible to contribute, for example, to theadjustment of flexibility of film that a plurality of the polymerizablecompounds containing S atom having different characteristics are usedtogether.

Specific examples of the polymerizable compound containing S atom areset forth below.

((D) Light-to-Heat Conversion Agent>

The light-to-heat conversion agent (D) according to the invention has anabsorption maximum wavelength in a range of 700 to 1,300 nm. In case ofperforming laser engraving of the resin composition for laser engravingaccording to the invention using a laser (YAG laser, semiconductorlaser, fiber laser or surface-emitting laser) emitting an infrared rayof 700 to 1,300 nm, the light-to-heat conversion agent (D) is employedas an infrared absorbing agent. The light-to-heat conversion agent (D)absorbs the laser light to generate heat and accelerates heatdecomposition of the resin composition. The light-to-heat conversionagent (D) for use in the invention includes dyes and pigments eachhaving an absorption maximum in a wavelength range of 700 to 1,300 nm.

As the dye, commercially available dyes and known dyes described inliteratures, for example, Senryo Binran (Dye Handbook) compiled by TheSociety of Synthetic Organic Chemistry, Japan (1970) can be used.Specifically, the dyes include azo dyes, metal complex azo dyes,pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes,phthalocyanine dyes, carbonium dyes, diimmonium compounds, quinoneiminedyes, methine dyes, cyanine dyes, squarylium dyes, pyrylium salts andmetal thiolate complexes.

Examples of preferable dye include cyanine dyes described, for example,in JP-A-58-125246, JP-A-59-84356, JP-A-59-202829 and JP-A-60-78787,methine dyes described, for example, in JP-A-58-173696, JP-A-58-181690and JP-A-58-194595, naphthoquinone dyes described, for example, inJP-A-58-112793, JP-A-58-224793, JP-A-59-48187, JP-A-59-73996,JP-A-60-52940 and JP-A-60-63744, squarylium dyes described, for example,in JP-A-58-112792, and cyanine dyes described, for example, in BritishPatent 434,875.

Also, near infrared absorbing sensitizers described in U.S. Pat. No.5,156,938 are preferably used. Further, substitutedarylbenzo(thio)pyrylium salts described in U.S. Pat. No. 3,881,924,trimethinethiapyrylium salts described in JP-A-57-142645 (correspondingto U.S. Pat. No. 4,327,169), pyrylium compounds described inJP-A-58-181051, JP-A-58-220143, JP-A-59-41363, JP-A-59-84248,JP-A-59-84249, JP-A-59-146063 and JP-A-59-146061, cyanine dyes describedin JP-A-59-216146, pentamethinethiopyrylium salts described in U.S. Pat.No. 4,283,475, and pyrylium compounds described in JP-B-5-13514 (theterm “JP-B” as used herein means an “examined Japanese patentpublication”) and JP-B-5-19702 are also preferably used. Otherpreferable examples of the dye include near infrared absorbing dyesrepresented by formulae (I) and (II) in U.S. Pat. No. 4,756,993.

Other preferable examples of the light-to-heat conversion agent (D)according to the invention include specific indolenine cyanine dyesdescribed in JP-A-2002-278057.

Of the dyes, cyanine dyes, squarylium dyes, pyrylium dyes, nickelthiolate complexes and indolenine cyanine dyes are preferred. Further,cyanine dyes and indolenine cyanine dyes are more preferred.

Specific examples of the cyanine dye preferably used in the inventioninclude those described in Paragraph Nos. [0017] to [0019] ofJP-A-2001-133969, Paragraph Nos. [0012] to [0038] of JP-A-2002-40638 andParagraph Nos. [0012] to [0023] of JP-A-2002-23360.

The dye represented by formula (d) or formula (e) shown below ispreferable from the standpoint of light-to-heat conversion property.

In formula (d), R²⁹ to R³² each independently represents a hydrogenatom, an alkyl group or an aryl group. R³³ and R³⁴ each independentlyrepresents an alkyl group, a substituted oxy group or a halogen atom. nand m each independently represents an integer of 0 to 4. R²⁹ and R³⁰ orR³¹ and R³² may be combined with each other to form a ring. Also, R²⁹and/or R³⁰ and R³³ or R³¹ and/or R³² and R³⁴ may be combined with eachother to form a ring. Further, when plural R³³s or R³⁴s are present, theR33s or R 34s may be combined with each other to form a ring. X² and X³each independently represents a hydrogen atom, an alkyl group or an arylgroup, provided that at least one of X² and X³ represents a hydrogenatom or an alkyl group. Q represents a trimethine group which may have asubstituent or a pentamethine group which may have a substituent or mayform a ring structure together with a divalent organic group. Zc⁻represents a counter anion. However, Zc⁻ is not necessary when the dyerepresented by formula (d) has an anionic substituent in the structurethereof and neutralization of charge is not needed. Preferable examplesof the counter ion for Zc⁻ include a halogen ion, a perchlorate ion, atetrafluoroborate ion, a hexafluorophosphate ion and a sulfonate ion,and particularly preferable examples thereof include a perchlorate ion,a hexafluorophosphate ion and an arylsulfonate ion in view of thepreservation stability of a coating solution for resin compositionlayer.

Specific examples of the dye represented by formula (d) preferably usedin the invention include those illustrated below.

In formula (e), R³⁵ to R⁵⁰ each independently represents a hydrogenatom, a halogen atom, a cyano group, an alkyl group, an aryl group, analkenyl group, an alkynyl group, a hydroxy group, a carbonyl group, athio group, a sulfonyl group, a sulfinyl group, an oxy group, an aminogroup or an onium salt structure. When a substituent can be introducedinto these groups, they may have the substituent. M represents twohydrogen atoms, a metal atom, a halometal group or an oxymetal group.Examples of the metal atom included therein include atoms of Groups IA,IIA, IIIB and IVB of the Periodic Table, transition metals of the first,second and third periods, and lanthanoid elements. Among them, copper,magnesium, iron, zinc, cobalt, aluminum, titanium and vanadium arepreferred.

Specific examples of the dye represented by formula (e) preferably usedin the invention include those illustrated below.

Examples of the pigment for use in the invention include commerciallyavailable pigments and pigments described in Colour Index (C.I.),Saishin Ganryo Binran (Handbook of the Newest Pigments) compiled byPigment Technology Society of Japan (1977), Saishin Ganryo Oyou Gijutsu(Newest Application on Technologies for Pigments), CMC Publishing Co.,Ltd. (1986) and Insatsu Ink Gijutsu (Printing Ink Technology), CMCPublishing Co., Ltd. (1984).

Examples of the pigment include black pigments, yellow pigments, orangepigments, brown pigments, red pigments, purple pigments, blue pigments,green pigments, fluorescent pigments, metal powder pigments andpolymer-bonded dyes. Specific examples of usable pigment includeinsoluble azo pigments, azo lake pigments, condensed azo pigments,chelated azo pigments, phthalocyanine pigments, anthraquinone pigments,perylene and perynone pigments, thioindigo pigments, quinacridonepigments, dioxazine pigments, isoindolinone pigments, quinophthalonepigments, dying lake pigments, azine pigments, nitroso pigments, nitropigments, natural pigments, fluorescent pigments, inorganic pigments andcarbon black. Of the pigments, carbon black is preferred.

The pigment may be used without undergoing surface treatment or may beused after the surface treatment. For the surface treatment, a method ofcoating a resin or wax on the surface, a method of attaching asurfactant and a method of bonding a reactive substance (for example, asilane coupling agent, an epoxy compound or polyisocyanate) to thepigment surface. The surface treatment methods are described in KinzokuSekken no Seishitsu to Oyo (Properties and Applications of Metal Soap),Saiwai Shobo, Insatsu Ink Gijutsu (Printing Ink Technology), CMCPublishing Co., Ltd. (1984), and Saishin Ganryo Oyo Gijutsu (NewestApplication on Technologies for Pigments), CMC Publishing Co., Ltd.(1986).

The pigment has a particle size of preferably from 0.01 to 10 μm, morepreferably from 0.05 to 1 μm, particularly preferably from 0.1 to 1 μm.When the particle size of the pigment is 0.01 μm or more, stability ofthe pigment dispersion in a coating solution increases and when it is 10μm or less, uniformity of the resin composition layer is good.

For dispersing the pigment, a known dispersion technique for use in theproduction of ink or toner may be used. Examples of the dispersingmachine include an ultrasonic dispersing machine, a sand mill, anattritor, a pearl mill, a super-mill, a ball mill, an impeller, adisperser, a KD mill, a colloid mill, a dynatron, a three roll mill anda pressure kneader. The dispersing machines are described in detail inSaishin Ganryo Oyo Gijutsu (Newest Application on Technologies forPigments), CMC Publishing Co., Ltd. (1986).

The cyanine compounds and phthalocyanine compounds are preferable in theinvention in view of high engraving sensitivity and the cyaninecompounds and phthalocyanine compounds are particularly preferable.Further, it is preferable to use a combination (condition) of thelight-to-heat conversion agent and the hydrophilic polymer in which heatdecomposition temperature of the light-to-heat conversion agent is sameas or higher than heat decomposition temperature of the hydrophilicpolymer, because the engraving sensitivity tends to increase.

Specific examples of the light-to-heat conversion agent for use in theinvention include cyanine dyes, for example, heptamethyne cyanine dyes,oxonol dyes, for example, pentamethyne oxonol dyes, indolium dyes,benzindolium dyes, benzothiazolium dyes, quinolinium dyes and phthalidecompounds reacted with developers. It is not necessary true that allcyanine dyes have the light absorbing properties described above. Thelight absorbing properties very largely vary according, for example, tothe kind and position of substituent in its molecule, number ofconjugate bond, kind of counter ion or surrounding environment in whichthe dye molecule is present. Further, ordinarily commercially availablelaser dyes, supersaturation absorption dyes and near infrared absorptiondyes may also be used. Examples of the laser dye include ADS740PP,ADS745HT, ADS760MP, ADS740WS, ADS765WS, ADS745HO, ADS790NH and ADS800NH,all trade names of American Dye Source, Inc. (Canada), and NK-3555,NK-3509 and NK-3519, all trade names of Hayashibara Biochemical Labs.,Inc. Examples of the near infrared absorption dye include ADS775MI,ADS775MP, ADS775HI, ADS775PI, ADS775PP, ADS780MT, ADS780BP, ADS793EI,ADS798MI, ADS798MP, ADS800AT, ADS805PI, ADS805PP, ADS805PA, ADS805PF,ADS812MI, ADS815EI, ADS818HI, ADS818HT, ADS822MT, AD830AT, ADS838MT,ADS840MT, ADS845BI, ADS905AM, ADS956BI, ADS1040T, ADS1040P, ADS1045P,ADS1050P, ADS1060A, ADS1065A, ADS1065P, ADS1100T, ADS1120F, ADS1120P,ADS780WS, ADS785WS, ADS790WS, ADS805WS, ADS820WS, ADS830WS, ADS850WS,ADS780HO, ADS810CO, ADS820HO, ADS821NH, ADS840NH, ADS880MC, ADS890MC andADS920MC, all trade names of American Dye Source, Inc. (Canada),YKR-2200, YKR-2081, YKR-2900, YKR-2100 and YKR-3071, all trade names ofYamamoto Chemicals Inc., SDO-1000B, trade name of Arimoto Chemical Co.,Ltd., NK-3508 and NKX-114, all trade names of Hayashibara BiochemicalLabs., Inc. However, the invention should no be construed as beinglimited thereto. As the phthalide compound reacted with developer, thosedescribed in Japanese Patent 3271226 may also be used. Further, aphosphoric ester metal compound, for example, complexes of phosphoricester and cupper salt described in JP-A-6-345820 and WO99/10354 may beused. Moreover, ultrafine particles having a light absorption propertyin a near infrared region and a number average particle size ofpreferably 0.3 μm or less, more preferably 0.1 μm or less, still morepreferably 0.08 μm or less, may be used. For instance, ultrafineparticles of metal oxide, for example, yttrium oxide, tin oxide and/orindium oxide, copper oxide or iron oxide and of metal, for example,gold, silver, palladium or platinum are illustrated. Moreover, fineparticles, for example, of glass having a number average particle sizeof preferably 5 μm or less, more preferably 1 μm or less, to which ametal ion, for example, ion of copper, tin, indium, yttrium, chromium,cobalt, titanium, nickel, vanadium or rare earth element is added mayalso be used. Furthermore, a dye which reacts with a photosensitiveresin composition to change its light absorption wavelength may beincorporated into microcapsules. In such a case, a number averageparticle size of the microcapsule is preferably 10 μm or less, morepreferably 5 μm or less, still more preferably 1 μm or less. Ionexchanger fine particles to which a metal ion, for example, ion ofcopper, tin, indium, yttrium or rare earth element is adsorbed may alsobe used. The ion exchanger fine particle may be an organic resin fineparticle or an inorganic fine particle. Examples of the inorganic fineparticle include fine particle of amorphous zirconium phosphate,amorphous zirconium silicate phosphate, amorphous zirconiumhexamethaphosphate, layered zirconium phosphate, reticular zirconiumphosphate, zirconium tungstate and zeolite. Examples of the organicresin fine particle include fine particle of ordinarily used ionexchange resin and ion exchange cellulose.

On the other hand, any carbon black can be used regardless of the use(for example, for color, for rubber or for dry cell) as well as carbonblack classified according to ASTM, as long as dispersion stability ofthe composition is not damaged. The carbon black includes, for example,furnace black, thermal black, channel black, lamp black and acetyleneblack. A black coloring agent, for example, carbon black can be used asa color chip or a color paste prepared by previously dispersing it innitrocellulose or a binder using a dispersing agent, if desired, inorder to facilitate dispersion. Such a color chip or a color paste iseasily available as a commercial product.

In the invention, it is possible to use carbon black having a relativelylow specific surface area and relatively low DBP absorptive capacity andfinely divided carbon black having high specific surface area.

Preferable examples of carbon black include Printex® U, Printex® A andSpezialschwarz® 4 (available from Degussa AG).

In the invention, conductive carbon black having the specific surfacearea of 150 m²/g or more and the DBP absorptive capacity of 150 ml/100 gor more is preferable from the standpoint of increase in engravingsensitivity resulting from efficiently transferring the heat generatedby light-to-heat conversion to the surrounding polymer or the like.

The specific surface area is more preferably 250 m²/g or more,particularly preferably 500 m²/g or more. The DBP absorptive capacity ismore preferably 200 ml/100 g or more, particularly preferably 250 ml/100g or more. The carbon black may be acidic carbon black or basic carbonblack. Carbon black is preferably basic carbon black.

Appropriate conductive carbon blacks having the specific surface area upto about 1,500 m²/g and the DBP absorptive capacity up to about 550ml/100 g are commercially available by the names of Ketjenblack® EC300Jand Ketjenblack® EC600J (available from Akzo), Printex® XE (availablefrom Degussa AG), Black Pearls® 2000 (available from Cabot Corp.) andKetjenblack (produced by Lion Corp.).

The concentration of the light-to-heat conversion agent added to theresin composition for laser engraving may be considerably varieddepending on the molecular extinction coefficient thereof inherent inthe molecule and is preferably in a range of 0.01 to 20% by weight, morepreferably in a range of 0.05 to 10% by weight, particularly preferablyin a range of 0.1 to 5% by weight, based on the total solid content ofthe resin composition.

<(E) Polymerization Initiator>

As the polymerization initiator, initiators known to those skilled inthe art can be used without limitation. Specifically, many compoundsdescribed in literature, for example, Bruce M. Monroe et al., ChemicalReview, 93, 435 (1993), R. S. Davidson, Journal of Photochemistry andBiology A: Chemistry, 73, 81 (1993), J. P. Faussier, PhotoinitiatedPolymerization-Theory and Applications: Rapra Review Vol. 9, Report,Rapra Technology (1998) or M. Tsunooka et al., Prog. Polym. Sci., 21, 1(1996) can be used. Further, a group of compounds undergoing oxidativeor reductive bond cleavage as described, for example, in F. D. Saeva,Topics in Current Chemistry, 156, 59 (1990), G. G. Maslak, Topics inCurrent Chemistry, 168, 1 (1993), H. B. Shuster et al., JACS, 112, 6329(1990) and I. D. F. Eaton et al., JACS, 102, 3298 (1980) are known.

With respect to specific examples of preferable initiator, a radicalpolymerization initiator which is a compound that generates a radicalupon light energy and/or heat energy and initiates or promotes apolymerization reaction of polymerizable compound is described ingreater detail below, but the invention should not be construed as beinglimited thereto.

As the radical polymerization initiator preferably used in theinvention, (a) an aromatic ketone, (b) an onium salt compound, (c) anorganic peroxide, (d) a thio compound, (e) a hexaarylbiimidazolecompound, (f) a ketoxime ester compound, (g) a borate compound, (h) anazinium compound, (i) a metallocene compound, (j) an active estercompound, (k) a compound having a carbon-halogen bond and (l) an azoseries compound. Specific examples of the compounds of (a) to (l) areset forth below, but the invention should not be construed as beinglimited thereto.

(a) Aromatic Ketone

The aromatic ketone (a) preferably used as the radical polymerizationinitiator in the invention includes compounds having a benzophenoneskeleton or a thioxantone skeleton described in J. P. Fouassier and J.F. Rabek, Radiation Curing in Polymer Science and Technology, pages 77to 117 (1993). For example, the following compounds are recited.

Among them, particularly preferable examples of the aromatic ketone (a)include the following compound:

(b) Onium Salt Compound

The onium salt compound (b) preferably used as the radicalpolymerization initiator in the invention includes compounds representedby the following formulae (1) to (3):

In formula (1), Ar¹ and Ar² each independently represent an aryl grouphaving not more than 20 carbon atoms, which may have a substituent.(Z²)⁻ represents a counter ion selected from the group consisting of ahalogen ion, a perchlorate ion, a carboxylate ion, tetrafluoroborateion, a hexafluorophosphate ion and a sulfonate ion, and is preferably aperchlorate ion, a hexafluorophosphate ion and an arylsulfonate ion.

In formula (2), Ar³ represents an aryl group having not more than 20carbon atoms, which may have a substituent. (Z³)⁻ represents a counterion having the same meaning as defined for (Z²)⁻.

In formula (3), R²³, R²⁴ and R²⁵, which may be the same or different,each represent a hydrocarbon group having not more than 20 carbon atoms,which may have a substituent. (Z⁴)⁻ represents a counter ion having thesame meaning as defined for (Z²)⁻.

Specific examples of the onium salt preferably used in the inventioninclude those described in Paragraph Nos. [0030] to [0033] ofJP-A-2001-133969 and Paragraph Nos. [0015] to [0046] ofJP-A-2001-343742, and specific aromatic sulfonium salt compoundsdescribed in JP-A-2002-148790, JP-A-2001-343742, JP-A-2002-6482,JP-A-2002-116539 and JP-A-2004-102031 both of which the applicant hasbeen previously proposed.

(c) Organic Peroxide

The organic peroxide (c) preferably used as the radical polymerizationinitiator in the invention includes almost all organic compounds havingat least one oxygen-oxygen bond in the molecules thereof. Specificexamples of the organic peroxide include methyl ethyl ketone peroxide,cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide,methylcyclohexanone peroxide, acetylacetone peroxide,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)butane,tert-butylhydroperoxide, cumene hydroperoxide, diisopropylbenzenehydroperoxide, paramethane hydroperoxide,2,5-dimethylhexane-2,5-dihydroperoxide, 1,1,3,3-tetramethylbutylhydroperoxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide,dicumyl peroxide, bis(tert-butylperoxyisopropyl)benzene,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-xanoyl peroxide,succinic peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide,methatoluoyl peroxide, diisopropylperoxy dicarbonate,di-2-ethylhexylperoxy dicarbonate, di-2-ethoxyethylperoxy dicarbonate,dimethoxyisopropylperoxy dicarbonate, di(3-methyl-3-methoxybutyl)peroxydicarbonate, tert-butylperoxy acetate, tert-butylperoxy pivalate,tert-butylperoxy neodecanoate, tert-butylperoxy octanoate,tert-butylperoxy 3,5,5-trimethylhexanoate, tert-butylperoxy laurate,tertiary carbonate,3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(tert-amylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(tert-hexylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(tert-octylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(cumylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(p-isopropylcumylperoxycarbonyl)benzophenone, carbonyldi(tert-butylperoxydihydrogen diphthalate) and carbonyldi(tert-hexylperoxydihydrogen diphthalate).

Among them, peroxy ester compounds, for example,3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(tert-amylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(tert-hexylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(tert-octylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(cumylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(p-isopropylcumylperoxycarbonyl)benzophenone anddi-tert-butyldiperoxy isophthalate are preferred.

(d) Thio Compound

The thio compound (d) preferably used as the radical polymerizationinitiator in the invention includes compounds having the structurerepresented by the following formula (4):

In formula (4), R²⁶ represents an alkyl group, an aryl group or asubstituted aryl group. R²⁷ represents a hydrogen atom or an alkylgroup. Alternatively, R²⁶ and R²⁷ combine with each other and togetherrepresent a non-metallic atomic group necessary for forming a5-membered, 6-membered or 7-membered ring, which may contain a heteroatom selected from an oxygen atom, a sulfur atom and a nitrogen atom.

Specific examples of the thio compound represented by formula (4)include the following compounds:

No. R²⁶ R²⁷ 1 —H —H 2 —H —CH₃ 3 —CH₃ —H 4 —CH₃ —CH₃ 5 —C₆H₅ —C₂H₅ 6—C₆H₅ —C₄H₉ 7 —C₆H₄Cl —CH₃ 8 —C₆H₄Cl —C₄H₉ 9 —C₆H₄—CH₃ —C₄H₉ 10—C₆H₄—OCH₃ —CH₃ 11 —C₆H₄—OCH₃ —C₂H₅ 12 —C₆H₄—OC₂H₅ —CH₃ 13 —C₆H₄—OC₂H₅—C₂H₅ 14 —C₆H₄—OCH₃ —C₄H₉ 15 —(CH₂)₂— 16 —(CH₂)₂—S— 17 —CH(CH₃)—CH₂—S—18 —CH₂—CH(CH₃)—S— 19 —C(CH₃)₂—CH₂—S— 20 —CH₂—C(CH₃)₂—S— 21 —(CH₂)₂—O—22 —CH(CH₃)—CH₂—O— 23 —C(CH₃)₂—CH₂—O— 24 —CH═CH—N(CH₃)— 25 —(CH₂)₃—S— 26—(CH₂)₂—CH(CH₃)—S— 27 —(CH₂)₃—O— 28 —(CH₂)₅— 29 —C₆H₄—O— 30—N═C(SCH₃)—S— 31 —C₆H₄—NH— 32

(e) Hexaarylbiimidazole Compound

The hexaarylbiimidazole compound (e) preferably used as the radicalpolymerization initiator in the invention includes lophine dimersdescribed in JP-B-45-37377 and JP-B-44-86516, specifically, for example,2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-bromophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o,p-dichlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetra(m-methoxyphenyl)biimidazole,2,2′-bis(o,o′-dichlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-nitrophenyl)-4,4′,5,5′-tetraphenylbiimidazole,2,2′-bis(o-methylphenyl)-4,4′,5,5′-tetraphenylbiimidazole and2,2′-bis(o-trifluoromethylphenyl)-4,4′,5,5′-tetraphenylbiimidazole.

(f) Ketoxime Ester Compound

The ketoxime ester compound (f) preferably used as the radicalpolymerization initiator in the invention includes, for example,3-benzoyloxyiminobutan-2-one, 3-acetoxyiminobutan-2-one,3-propyonyloxyiminobutan-2-one, 2-acetoxyiminopentan-3-one,2-acetoxyimino-1-phenylpropan-1-one,2-benzoyloxyimino-1-phenylpropan-1-one,3-p-toluenesulfonyloxyiminobutan-2-one and2-ethoxycarbonyloxyimino-1-phenylpropan-1-one.

(g) Borate Compound

The borate compound (g) preferably used as the radical polymerizationinitiator in the invention includes compounds represented by thefollowing formula (5):

In formula (5), R²⁸, R²⁹, R³⁰ and R³¹, which may be the same ordifferent, each represents a substituted or unsubstituted alkyl group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted alkynyl group or asubstituted or unsubstituted heterocyclic group, or at least two of R²⁸,R²⁹, R³⁰ and R³¹ may be combined with each other to form a cyclicstructure, provided that at least one of R²⁸, R²⁹, R³⁰ and R³¹represents a substituted or unsubstituted alkyl group. (Z⁵)⁺ representsan alkali metal cation or a quaternary ammonium cation.

Specific examples of the compound represented by formula (5) includecompounds described in U.S. Pat. Nos. 3,567,453 and 4,343,891, EuropeanPatents 109,772 and 109,773, and the following compounds:

(h) Azinium Compound

The azinium compound (h) preferably used as the radical polymerizationinitiator in the invention includes compounds having an N—O bonddescribed in JP-A-63-138345, JP-A-63-142345, JP-A-63-142346,JP-A-63-143537 and JP-B-46-42363.

(i) Metallocene Compound

The metallocene compound (i) preferably used as the radicalpolymerization initiator in the invention includes titanocene compoundsdescribed in JP-A-59-152396, JP-A-61-151197, JP-A-63-41484, JP-A-2-249and JP-A-2-4705, and iron-arene complexes described in JP-A-1-304453 andJP-A-1-152109.

Specific examples of the titanocene compound includedicyclopentadienyl-Ti-dichloride, dicyclopentadienyl-Ti-biphenyl,dicyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl,dimethylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,dimethylcyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,dimethylcyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl,bis(cyclopentadienyl)bis[2,6-difluoro-3-(pyr-1-yl)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(methylsulfonamido)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-butylpivaloylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-butyl-(4-chlorobenzoyl)amino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-benzyl-2,2-dimethylpentanoylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-(2-ethylhexyl)-4-tolylsulfonylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-(3-oxaheptyl)benzoylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-(3,6-dioxadecyl)benzoylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(trifluoromethylsulfonylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(trifluoroacetylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(2-chlorobenzoylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(4-chlorobenzoylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-(3,6-dioxadecyl)-2,2-dimethylpentanoylamino)phenyl]titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-(3,7-dimethyl-7-methoxyoctyl)benzoylamino)phenyl]titaniumandbis(cyclopentadienyl)bis[2,6-difluoro-3-(N-cyclohexylbenzoylamino)phenyl]titanium.

(j) Active Ester Compound

The active ester compound (j) preferably used as the radicalpolymerization initiator in the invention includes imidosulfonatecompounds described in JP-B-62-6223, and active sulfonates described inJP-B-63-14340 and JP-A-59-174831.

(k) Compound having a Carbon-Halogen Bond

The compound having a carbon-halogen bond (k) preferably used as theradical polymerization initiator in the invention includes the compoundsrepresented by the following formulae (6) to (12):

In formula (6), X² represents a halogen atom, Y¹ represents —C(X² )₃,—NH₂, —NHR³⁸, —N(R³⁸)₂ or —OR³⁸, R³⁸ represents an alkyl group, asubstituted alkyl group, an aryl group or a substituted aryl group, andR³⁷ represents —C(X²)₃, an alkyl group, a substituted alkyl group, anaryl group, a substituted aryl group or a substituted alkenyl group.

In formula (7), R³⁹ represents an alkyl group, a substituted alkylgroup, an alkenyl group, a substituted alkenyl group, an aryl group, asubstituted aryl group, a halogen atom, an alkoxy group, a substitutedalkoxy group, a nitro group or a cyano group, X³ represents a halogenatom, and n represents an integer of 1 to 3.

R⁴⁰-Z⁶-CH_((2-m))(X³)_(m)R⁴¹   Formula (8)

In formula (8), R⁴⁰ represents an aryl group or a substituted arylgroup, R⁴¹ represents a group shown below or a halogen atom, Z⁶represents —C(═O)—, —C(═S)— or —SO₂—, X³ represents a halogen atom, andm represents 1 or 2.

wherein R⁴² and R⁴³ each represents an alkyl group, a substituted alkylgroup, an alkenyl group, a substituted alkenyl group, an aryl group or asubstituted aryl group, and R⁴⁴ has the same meaning as defined for R³⁸in formula (6).

In formula (9), R⁴⁵ represents an aryl group which may be substituted ora heterocyclic group which may be substituted, R⁴⁶ represents atrihaloalkyl group or trihaloalkenyl group each having from 1 to 3carbon atoms, and p represents 1, 2 or 3.

In formula (10), which represents a carbonylmethylene heterocycliccompound having a trihalogenomethyl group, L⁷ represents a hydrogen atomor a group represented by formula —CO—(R⁴⁷)_(q)(C(X⁴)₃)_(r), Q²represents a sulfur atom, a selenium atom, an oxygen atom, adialkylmethylene group, an alken-1,2-ylene group, a 1,2-phenylene groupor —N(—R⁴⁸)—, M⁴ represents a substituted or unsubstituted alkylenegroup, a substituted or unsubstituted alkenylene group or a 1,2-arylenegroup, R⁴⁸ represents an alkyl group, an aralkyl group or an alkoxyalkylgroup, R⁴⁷ represents a divalent carbocyclic or heterocyclic aromaticgroup, X⁴ represents a chlorine atom, a bromine atom or an iodine atom,q represents 0 or 1, and r represents 1 or 2, provided that when qrepresents 0, r represents 1, and when q represents 1, r represents 1 or2.

In formula (11), which represents a4-halogeno-5-(halogenomethylphenyl)oxazole derivative, X⁵ represents ahalogen atom, t represents an integer of 1 to 3, s represents an integerof 1 to 4, R⁴⁹ represents a hydrogen atom or —CH_(3-t)X⁵ _(t), and R⁵⁰represents an s-valent unsaturated organic residue, which may besubstituted.

In formula (12), which represents a2-(halogenomethylphenyl)-4-halogenooxazole derivative, X⁶ represents ahalogen atom, v represents an integer of 1 to 3, u represents an integerof 1 to 4, R⁵¹ represents a hydrogen atom or —CH_(3-v)X⁶ _(v), and R⁵²represents an u-valent unsaturated organic residue, which may besubstituted.

Specific examples of the compound having a carbon-halogen bond includecompounds described in Wakabayashi et al., Bull. Chem. Soc. Japan, Vol.42, 2924 (1969), for example,2-phenyl-4,6-bis(trichloromethyl)-S-triazine,2-(p-chlorophenyl)-4,6-bis(trichloromethyl)-S-triazine,2-(p-tolyl)-4,6-bis(trichloromethyl)-S-triazine,2-(p-methoxyphenyl)-4,6-bis(trichloromethyl)-S-triazine,2-(2′,4′-dichlorophenyl)-4,6-bis(trichloromethyl)-S-triazine,2,4,6-tris(trichloromethyl)-S-triazine,2-methyl-4,6-bis(trichloromethyl)-S-triazine,2-n-nonyl-4,6-bis(trichloromethyl)-S-triazine and2-(α,α,β-trichloroethyl)-4,6-bis(trichloromethyl)-S-tiazine. Further,compounds described in British Patent 1,388,492, for example,2-styryl-4,6-bis(trichloromethyl)-S-triazine,2-(p-methylstyryl)-4,6-bis(trichloromethyl)-S-triazine,2-(p-methoxylstyryl)-4,6-bis(trichloromethyl)-S-triazine and2-(p-methoxylstyryl)-4-amino-6-trichloromethyl-S-triazine, compoundsdescribed in JP-A-53-133428, for example,2-(4-methoxynaphth-1-yl)-4,6-bis(trichloromethyl)-S-triazine,2-(4-ethoxynaphth-1-yl)-4,6-bis(trichloromethyl)-S-triazine,2-[4-(2-ethoxyethyl)naphth-1-yl]-4,6-bis(trichloromethyl)-S-triazine,2-(4,7-dimethoxynaphth-1-yl)-4,6-bis(trichloromethyl)-S-triazine and2-(acenaphth-5-yl)-4,6-bis(trichloromethyl)-S-triazine, and compoundsdescribed in German Patent 3,337,024, for example, the compounds shownbelow are exemplified. Moreover, compounds which can be easilysynthesized by one skilled in the art according to synthesis methodsdescribed in M. P. Hutt, E. F. Elslager and L. M. Herbel, Journal ofHeterocyclic Chemistry, Vol. 7, No. 3, page 511 et seq. (1970), forexample, the compounds shown below are exemplified.

(l) Azo Series Compound

The azo series compound (l) preferably used as the radicalpolymerization initiator in the invention includes, for example,2,2′-azobisisobutyronitrile, 2,2′-azobispropionitrile,1,1′-azobis(cyclohexane-1-carbonitrile),2,2′-azobis(2-methylbutyronitrile),2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),4,4′-azobis(4-cyanovaleric acid), dimethyl 2,2′-azobisisobutyrate,2,2′-azobis(2-methypropionamidooxime),2,2′-azobis[2-(2-imidazolin-2-yl)propane], 2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide},2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2′-azobis(N-butyl-2-methylpropionamide),2,2′-azobis(N-cyclohexyl-2-methylpropionamide),2,2′-azobis[N-(2-propenyl)-2-methylpropionamide] and2,2′-azobis(2,4,4-trimethylpentane).

More preferable examples of the radical polymerization initiator for usein the invention include the above-described aromatic ketone (a), oniumsalt compound (b), organic peroxide (c), hexaarylbiimidazole compound(e), metallocene compound (i) and compound having a carbon-halogen bond(k), and most preferable examples of the radical initiator include thearomatic iodonium salt, aromatic sulfonium salt, titanocene compound andtrihalomethyl-S-triazine compound represented by formula (6) describedabove.

The polymerization initiator can be added to the resin composition forlaser engraving containing a polymerizable compound preferably from 0.01to 10% by weight, more preferably from 0.1 to 3% by weight, based on thetotal solid content of the resin composition.

The polymerization initiators can be preferably used individually or incombination of two or more thereof in the invention.

<(F) Plasticizer>

Examples of the plasticizer (F) include dioctyl phthalate, didodecylphthalate, triethylene glycol dicaprylate, methyl glycol phthalate,tricresyl phosphate, dioctyl adipate, dibutyl sebacate and triacetylglycerol. Also, a polyethylene glycol or a polypropylene glycol (monooltype or diol type) is also used as the plasticizer.

The plasticizer has a function of making a relief-forming layer flexibleand should have good compatibility with the binder polymer. In general,a compound having high hydrophilicity has good compatibility with thebinder polymer. Of the compound having high hydrophilicity, a compoundhaving a structure alternately comprising a hydrophilic group and ahydrophobic group, for example, an ether compound containing a heteroatom in a straight chain or a secondary amine is preferably used. Thisis because the existence of hydrophilic group, for example, —O— or —NH—expresses the compatibility with a PVA derivative and the hydrophobicgroup other than the hydrophilic group weakens the intermolecular forceof PVA derivative to act for increase in the flexibility. Also, acompound having a small number of hydroxy groups capable of forming ahydrogen atom between the PVA derivative is preferably used. Examples ofsuch compound include ethylene glycol, propylene glycol and a dimer,trimer, homomultimer or comultimer including tetramer or more thereofand a secondary amine, for example, diethanolamine or dimethylolamine.Among them, ethylene glycols (including monomer, dimer, trimer andmultimer) which have small steric hindrance, are excellent incompatibility and have lower toxicity are particularly preferably usedas the plasticizer (F).

The ethylene glycols are roughly separated into three classes dependingon the molecular weight thereof. The first class includes ethyleneglycol which is a monomer. The second class includes diethylene glycolwhich is a dimer and triethylene glycol which is a trimer. The thirdclass includes polyethylene glycol including a tetramer or more. Thepolyethylene glycols are often marketed under trade names indicating theaverage molecular weight thereof in the suffix position. Thepolyethylene glycols are broadly classified into liquid polyethyleneglycols having a molecular weight of 200 to 700 and solid polyethyleneglycols having a molecular weight of 1,000 or more.

As a result of the intensive investigations, it has been found that asthe plasticizer has lower molecular weight, it has the larger effect ofmaking the resin flexible. For this reason, particularly, ethyleneglycol in the first class, diethylene glycol and triethylene glycol inthe second group and tetraethylene glycol (tetramer) included in thethird class are preferably used. Among them, diethylene glycol,triethylene glycol and tetraethylene glycol are more preferably used asthe plasticizer (F) from the standpoint of lower toxicity and excellenthandling property because of free from extraction from the resincomposition. Mixtures of two or more thereof are also preferably used.

The plasticizer can be added in an amount of 10% by weight or less basedon the total solid content of the resin composition for laser engraving.

<Additives for Assisting Heat Transfer>

When a substance having high thermal conductivity is added for thepurpose of assisting heat transfer, the engraving sensitivity furtherincreases. As an inorganic compound (metal particle), gold fineparticle, silver fine particle and copper fine particle each having aparticle diameter of micrometer order to several nanometer order arepreferable. As an organic compound, a polymer ordinarily known as aconductive polymer is preferable.

In particular, of the conductive polymers, polyaniline, polythiophene,polyisothianaphthene, polypyrrole, polyethylenedioxythiophene,polyacetylene and derivatives thereof are preferable, and in view ofhigh sensitivity, polyaniline, polythiophene, polyethylenedioxythiopheneand derivatives thereof are more preferable, polyaniline is particularlypreferable. The polyaniline may be added in any form of emeraldine baseand emeraldine salt and is preferably added in the form of emeraldinesalt in view of high heat transfer efficiency.

According to a preferred embodiment of the invention, a combination useof the polyester (A), for example, polylactic acid and the hydrophilicpolymer, for example, PVA is exemplified as described above. In such acase, since a solvent for preparing the composition is water or analcoholic solvent, it is preferred that the conductive polymer is addedin the form of an aqueous dispersion or aqueous solution to improvecompatibility between the polyester (A) and the hydrophilic polymer, forexample, PVA, from the standpoint of achieving high film strength andincrease in engraving sensitivity resulting from the improvement in heattransfer efficiency.

Specific examples of the metal particle and conductive polymer includethose described in catalogs of reagent maker, for example, AldrichCorp., Wako Pure Chemical Industries, Ltd. or Tokyo Chemical IndustryCo., Ltd.

From the standpoint of the improvement in heat transfer efficiency, mostpreferable conductive polymers include aquqPASS-OlX (produced byMitsubishi Rayon Co., Ltd.), Panipol-W (produced by Panipol Ltd.) andPanipol-F (produced by Panipol Ltd.).

<Additives for Increasing Engraving Sensitivity>

It is more preferable to add nitrocellulose to the resin composition asthe additive for the purpose of increasing the engraving sensitivity.Since the nitrocellulose is a self-reactive compound, it generates heatand assists heat decomposition of the coexisting hydrophilic polymer atthe time of laser engraving. As a result, it is believed that theengraving sensitivity increases.

The kind of nitrocellulose used is not particularly restricted as longas it is decomposable upon heat and may be any of RS (regular soluble)type, SS (spirit soluble) type and AS (alcohol soluble) type. Thenitrogen content of nitrocellulose is ordinarily approximately from 10to 14% by weight, preferably approximately from 11 to 12.5% by weight,more preferably approximately from 11.5 to 12.2% by weight. Thepolymerization degree of nitrocellulose can also be selected in a widerange, for example, of 10 to 1,500. The polymerization degree ofnitrocellulose is preferably approximately from 10 to 900, particularlypreferably approximately from 15 to 150. Preferable examples of thenitrocellulose include nitrocellulose having solution viscosityapproximately from 20 to 1/10 second, preferably approximately from 10to ⅛ second, as determined in accordance with JIS K6703 “Nitrocellulosefor industry use” (the viscosity expression of Hercules Powder Co.).Nitrocellulose having the solution viscosity approximately from 5 to ⅛second, particularly approximately from 1 to ⅛ second, is used in manycases. As the nitrocellulose used for forming the resin composition forlaser engraving, nitrocellulose of RS type soluble in an ester, forexample, ethyl acetate, a ketone, for example, methyl ethyl ketone ormethyl isobutyl ketone or an ether, for example, cellosolve (forexample, nitrocellulose having the nitrogen content approximately from11.7 to 12.2) is used in many cases. Two or more kinds of nitrocellulosemay be used in mixture, if desired.

The amount of nitrocellulose used may be selected in a range notdecreasing the sensitivity of resin composition for laser engraving andit is ordinarily approximately from 5 to 300 parts by weight, preferablyapproximately from 20 to 250 parts by weight, more preferablyapproximately from 50 to 200 parts by weight, based on 100 parts byweight of the binder polymer and the polymerizable compound (C). Thenitrocellulose is used in an amount approximately from 40 to 200 partsby weight in many cases.

<Co-Sensitizer>

The sensitivity at the photo-curing of the resin composition for laserengraving can be further improved by using a certain additive(hereinafter referred to as a “co-sensitizer”). The operation mechanismof the co-sensitizer is not quite clear but may be considered to bemostly based on the following chemical process. Specifically, theco-sensitizer reacts with various intermediate active species (forexample, a radical or a cation) generated during the process ofphoto-reaction initiated by the photopolymerization initiator andsubsequent addition-polymerization reaction to produce new activeradicals. The co-sensitizers are roughly classified into (a) compoundwhich is reduced to produce an active radical, (b) compound which isoxidized to produce an active radical and (c) compound which reacts witha radical having low activity to convert it into a more highly activeradical or acts as a chain transfer agent. However, in many cases, acommon view about which an individual compound belongs to which type isnot present.

(a) Compound which is Reduced to Produce an Active RadicalCompound having Carbon-Halogen Bond:

An active radical is considered to be generated by the reductivecleavage of the carbon-halogen bond. Specific examples of the compoundpreferably used include a trihalomethyl-s-triazine and atrihalomethyloxadiazole.

Compound having Nitrogen-Nitrogen Bond:

An active radical is considered to be generated by the reductivecleavage of the nitrogen-nitrogen bond. Specific examples of thecompound preferably used include a hexaarylbiimidazole.

Compound having Oxygen-Oxygen Bond:

An active radical is considered to be generated by the reductivecleavage of the oxygen-oxygen bond. Specific examples of the compoundpreferably used include an organic peroxide.

Onium Compound:

An active radical is considered to be generated by the reductivecleavage of a carbon-hetero bond or oxygen-nitrogen bond. Specificexamples of the compound preferably used include a diaryliodonium salt,a triarylsulfonium salt and an N-alkoxypyridinium (azinium) salt.

Ferrocene and Iron-Arene Complexes:

An active radical can be reductively produced.

(b) Compound which is Oxidized to Produce an Active Radical

Alkylate Complex:

An active radical is considered to be produced by the oxidative cleavageof a carbon-hetero bond. Specific examples of the compound preferablyused include a triaryl alkyl borate.

Alkylamine Compound:

An active radical is considered to be produced by the oxidative cleavageof a C-X bond on the carbon adjacent to nitrogen, wherein X ispreferably a hydrogen atom, a carboxyl group, a trimethylsilyl group ora benzyl group. Specific examples of the compound include anethanolamine, an N-phenylglycine and an N-trimethylsilylmethylaniline.

Sulfur-Containing or Tin-Containing Compound:

A compound in which the nitrogen atom of the above-described aminecompound is replaced by a sulfur atom or a tin atom is considered toproduce an active radical in the same manner. Also, a compound having anS—S bond is known to effect sensitization by the cleavage of the S—Sbond.

α-Substituted Methylcarbonyl Compound:

An active radical can be generated by the oxidative cleavage ofcarbonyl-a-carbon bond. The compound in which the carbonyl is convertedinto an oxime ether also shows the similar function. Specific examplesof the compound include an2-alkyl-1-[4-(alkylthio)phenyl]-2-morpholinopronone-1 and an oxime etherobtained by a reaction of the2-alkyl-1-[4-(alkylthio)phenyl]-2-morpholinopronone-1 with ahydroxyamine and subsequent etherification of the N—OH.

Sulfinic Acid Salt:

An active radical can be reductively produced. Specific examples of thecompound include sodium arylsulfinate.

(c) Compound which Reacts with a Radical to Convert it into a moreHighly Active Radical or Acts as a Chain Transfer Agent:

For example, a compound having SH, PH, SiH or GeH in its molecule isused as the compound. The compound donates hydrogen to a low activeradical species to produce a radical or is oxidized and deprotonized toproduce a radical. Specific examples of the compound include a2-mercaptobenzothiazole, a 2-mercaptobenzoxazole and a2-mercaptobenzimidazole.

A large number of examples of the co-sensitizer are more specificallydescribed, for example, in JP-A-9-236913 as additives for the purpose ofincreasing sensitivity, and they can be used in the invention. Some ofthem are set forth below, but the invention should not be construed asbeing limited thereto. In the formulae below, -TMS indicates atrimethylsilyl group.

Similarly to the light-to-heat conversion agent (D) described above, theco-sensitizer can be subjected to various chemical modifications so asto improve the characteristics of the resin composition for laserengraving. For instance, methods, for example, binding to thelight-to-heat conversion agent (D), polymerizable compound (C) or otherpart, introduction of a hydrophilic site, introduction of a substituentfor improving compatibility or inhibiting deposition of crystal,introduction of a substituent for improving an adhesion property, andformation of a polymer, may be used.

The co-sensitizers may be used individually or in combination of two ormore thereof. The amount of the co-sensitizer used is ordinarily from0.05 to 100 parts by weight, preferably from 1 to 80 parts by weight,more preferably from 3 to 50 parts by weight, per 100 parts by weight ofthe polymerizable compound (C).

<Polymerization Inhibitor>

It is preferred to add a small amount of a thermal polymerizationinhibitor to the resin composition according to the invention inaddition to the above-described components, in order to preventundesirable thermal polymerization of the polymerizable compound (C)during the production or preservation of the resin composition. Suitableexamples of the thermal polymerization inhibitor include hydroquinone,p-methoxyphenol, di-tert-butyl-p-cresol, pyrogallol, tert-butylcatechol,benzoquinone, 4,4′-thiobis(3-methyl-6-tert-butylphenol),2,2′-methylenebis(4-methyl-6-tert-butylphenol) andN-nitrosophenylhydroxyamine cerium(III) salt. Also, as thepolymerization inhibitor, Q-1301 (10% tricresyl phosphate solution,produced by Wako Pure Chemical Industries, Ltd.) is preferably usedbecause of extremely excellent stability at the preparation of resinprinting plate precursor for laser engraving having a relief-forminglayer using the resin composition according to the invention and thepreservation thereof. When this compound is used in combination with thepolymerizable compound (C) described above, the dramatically excellentpreservation stability of the resin printing plate precursor for laserengraving and the good laser engraving sensitivity can be obtained. Theamount of the thermal polymerization inhibitor added is preferably fromabout 0.01 to about 5% by weight based on the total amount of the resincomposition for laser engraving. In order to avoid polymerizationinhibition due to oxygen, a higher fatty acid derivative, for example,behenic acid or behenic amide may be added and allowed to localize onthe resin composition layer surface during the drying step after thecoating thereof on a support, if desired. The amount of the higher fattyacid derivative added is preferably from about 0.5 to about 10% byweight based on the total amount of the resin composition.

<Coloring Agent>

A coloring agent, for example, a dye or a pigment may further be addedfor the purpose of coloring the resin composition for laser engraving.By the coloring, properties, for example, visibility of the image areaor aptitude for an image density measurement apparatus can be improved.A pigment is preferably used as the coloring agent. Specific examplesthe coloring agent include a pigment, for example, a phthalocyaninepigment, an azo pigment, carbon black or titanium oxide, and a dye, forexample, Ethyl Violet, Crystal Violet, an azo dye, an anthraquinone dyeor a cyanine dye. The amount of the coloring agent added is preferablyfrom about 0.5 to about 5% by weight based on the total amount of theresin composition.

<Other Additive>

Further, a known additive, for example, a filler may be added forimproving physical properties of the cured layer of the resincomposition for laser engraving.

Examples of the filler include carbon black, carbon nanotube, fullerene,graphite, silica, alumina, aluminum and calcium carbonate. The fillersmay be used individually or as a mixture.

[Resin Printing Plate Precursor for Laser Engraving]

The resin printing plate precursor for laser engraving according to theinvention has on a support, a relief-forming layer comprising the resincomposition for laser engraving according to the invention. When acrosslinkable resin composition is used as the resin composition forlaser engraving, a crosslinkable relief-forming layer can be obtained.The resin printing plate precursor for laser engraving may further havean adhesive layer between the support and the relief-forming layer, anda slip coat layer and a protective film on the relief-forming layer, ifdesired.

In the resin printing plate precursor for laser engraving according tothe invention, the relief-forming layer is crosslinked and then laserengraving is conducted to prepare a relief printing plate. By thecrosslinkage of the relief-forming layer, abrasion of the relief-forminglayer at the time of printing can be prevented and a relief printingplate having a sharp configuration after the laser engraving can beobtained.

The content of the binder polymer in the relief-forming layer ispreferably from 30 to 80% by weight, more preferably from 40 to 70% byweight, based on the total solid content of the relief-forming layer.This is because when the content of the binder polymer is regulated to30% by weight or more, it is possible to prevent cold flow of theprinting plate precursor, whereas when the content of the binder polymeris regulated to 80% by weight or less, the printing durabilitysufficient for using as the relief printing plate is obtained withoutaccompanying the lack of other components.

The content of the polymerization initiator (E) in the relief-forminglayer is preferably from 0.01 to 10% by weight, more preferably from 0.1to 3% by weight, based on the total solid content of the relief-forminglayer. This is because when the content of the polymerization initiator(E) is regulated to 0.01% by weight or more, crosslinkage of thecrosslinkable relief-forming layer is promptly performed, whereas whenthe content of the polymerization initiator (E) is regulated to 10% byweight or less, the printing durability sufficient for using as therelief printing plate is obtained without accompanying the lack of othercomponents.

The content of the polymerizable compound (C) in the relief-forminglayer is preferably from 10 to 60% by weight, more preferably from 15 to40% by weight, based on the total solid content of the relief-forminglayer. This is because when the content of the component (C) isregulated to 10% by weight or more, the printing durability sufficientfor using as the relief printing plate is obtained, whereas when thecontent of the component (C) is regulated to 60% by weight or less, thestrength sufficient for using as the relief printing plate is obtained.

The relief-forming layer is obtained by molding the resin composition inthe shape of a sheet or a sleeve.

The material for use in the support of the resin printing plateprecursor for laser engraving according to the invention is notparticularly restricted and that having high dimensional stability ispreferably used. Examples of the material include metal, for example,steel, stainless or aluminum, a plastic resin, for example, a polyester(e.g., PET, PBT or PAN) or polyvinyl chloride, a synthetic rubber, forexample, styrene-butadiene rubber, and a plastic resin (for example, anepoxy resin or a phenol resin) enforced with glass fiber. As the supportfor the relief printing plate precursor, a PET (polyethyleneterephthalate) film or a steel substrate is preferably used. The shapeof the support is determined according to whether the relief-forminglayer is a sheet form or a sleeve form.

Between the relief-forming layer and the support, an adhesive layer maybe provided for the purpose of strengthening the adhesion propertytherebetween. The material for use in the adhesive layer may be amaterial which can strengthen the adhesion property after thecrosslinkage of the relief-forming layer and it is preferable to havethe strong adhesion property also before the crosslinkage of therelief-forming layer. The term “adhesion property” as used herein meansboth an adhesion property between the support and the adhesive layer andan adhesion property between the adhesive layer and the relief-forminglayer.

With respect to the adhesion property between the support and theadhesive layer, the peel forth per one cm width of a sample ispreferably 1.0 N/cm or more or unpeelable, more preferably 3.0 N/cm ormore or unpeelable, when the adhesive layer and the relief-forming layerare peeled from a laminate of support/adhesive layer/relief-forminglayer at a rate of 400 mm/sec.

With respect to the adhesion property between the adhesive layer and therelief-forming layer, the peel forth per one cm width of a sample ispreferably 1.0 N/cm or more or unpeelable, more preferably 3.0 N/cm ormore or unpeelable, when the adhesive layer is peeled from a laminate ofadhesive layer/relief-forming layer.

The relief-forming layer constitutes a portion where a relief is formedafter the laser engraving and the surface of the relief functions as anink-receptive area. Since the relief-forming layer after thecrosslinkage is strengthened by the crosslinkage, scratch or dent whichadversely affects printing on the surface of the relief-forming layerhardly occurs. However, the relief-forming layer before the crosslinkageis insufficient in the strength in many cases and the scratch or dent isapt to be formed on the surface thereof. Thus, in order to prevent theoccurrence of scratch or dent on the surface of the relief-forminglayer, a protective film may be provided on the surface of therelief-forming layer.

When the protective film is too thin, the effect of preventing theoccurrence of scratch or dent is not obtained and whereas, it is toothick, its handling is inconvenient and the cost increases. Therefore,the thickness of the protective film is preferably from 25 to 500 μm,more preferably from 50 to 200 μm.

As the protective film, a material known for a protective film forprinting plate, for example, a polyester film, e.g., PET (polyethyleneterephthalate) film or a polyolefin film, e.g., PE (polyethylene) filmor PP (polypropylene) film can be used. The surface of the protectivefilm may be plain or matted.

In the case of providing the protective film on the relief-forminglayer, the protective film should be peelable. When the protective filmis unpeelable or on the contrary when it is difficult to adhere on therelief-forming layer, a slip coat layer may be provided between theprotective film and the relief-forming layer.

As the material for use in the slip coat layer, it is preferred that aresin which is soluble or dispersible in water and has low tackiness,for example, polyvinyl alcohol, polyvinyl acetate, partially saponifiedpolyvinyl alcohol, hydroxyalkyl cellulose, alkyl cellulose or polyamideresin is mainly used. Of the resins, partially saponified polyvinylalcohol having a saponification degree of 60 to 99% by mole,hydroxyalkyl cellulose including the alkyl group having from 1 to 5carbon atoms and alkyl cellulose including the alkyl group having from 1to 5 carbon atoms are particularly preferably used in view of thetackiness.

With respect to the peelability of the protective film, the peel forthper one cm width of a sample is preferably from 5 to 200 mN/cm, morepreferably from 10 to 150 mN/cm, when the protective film is peeled froma laminate of relief-forming layer (and a slip coat layer)/protectivefilm at a rate of 200 mm/sec. When the peel forth is 5 mN/cm or more,the protective film is prevented from peeling while at work and whereas,when the peel forth is 200 mN/cm or less, the protective film can bereasonably peeled.

Now, a method of producing the resin printing plate precursor for laserengraving is described below. The producing method is not particularlyrestricted and includes, for instance, a method wherein a solution ofthe resin composition for laser engraving is prepared, the solvent isremoved from the solution and then the composition is subjected to meltextrusion on a support. Alternatively, a method wherein the solution ofthe resin composition for laser engraving is cast on a support and thesolvent is removed from the solution by drying in an oven may be used.

Then, a protective film may be laminated on the relief-forming layer, ifdesired. The lamination can be performed by pressure bonding of theprotective film to the relief-forming layer by means of a heatedcalendar roll or by bringing the protective film into close contact withthe relief-forming layer impregnated with a small amount of a solvent inits surface.

In the case of using the protective film, a method wherein therelief-forming layer is firstly laminated on the protective film andthen the support is laminated on the relief-forming layer may beadopted.

In the case of providing the adhesive layer, it can be responded byusing a support having the adhesive layer coated thereon. In the case ofproviding the slip coat layer, it can be responded by using a protectivefilm having the slip coat layer coated thereon.

The solution of the resin composition for laser engraving can beproduced, for example, by dissolving the binder polymer and, if desired,a plasticizer in an appropriate solvent and then dissolving thepolymerization initiator (E) and the polymerizable compound (C) in theresulting solution. Since most of the solvent component is necessary tobe removed at the stage of the production of printing plate precursor,it is preferred to use an easily volatile solvent, for example, a lowmolecular alcohol (e.g., ethanol) and to control the total amount of thesolvent added as small as possible. By increasing the temperature of thesystem, the amount of the solvent added can be reduced. However, sincethe polymerizable compound (C) is apt to undergo polymerization reactionwhen the temperature is too high, the preparation temperature of thesolution after adding the polymerizable compound (C) and/or thepolymerization initiator (E) is preferably from 30 to 80° C.

It is preferred that the relief-forming layer according to the inventionhas thickness of 0.05 mm or more before and after the crosslinkage, andit is more preferred that the relief-forming layer according to theinvention has thickness of 0.05 mm or more after the crosslinkage. Fromthe standpoint of satisfying various flexographic printing aptitudes,for example, abrasion resistance or ink transfer property, the thicknessof the relief-forming layer on the printing plate (corresponding to thethickness of the relief-forming layer after the crosslinkage) ispreferably from 0.05 to 10 mm, more preferably from 0.05 to 7 mm,particularly preferably from 0.05 to 0.3 mm.

[Relief Printing Plate and Production Thereof]

The resin printing plate precursor for laser engraving thus-obtained canproduce a relief printing plate according to the sequential processesdescribed below.

First example comprises (1a) a process of irradiating the resin printingplate precursor for laser engraving with an active ray to crosslink therelief-forming layer and (2) a process of laser engraving thecrosslinked relief-forming layer.

Second example comprises (1b) a process of heating the resin printingplate precursor for laser engraving to crosslink the relief-forminglayer and (2) a process of laser engraving the crosslinkedrelief-forming layer.

The processes (1a) and (1b) may be used together simultaneously orsuccessively.

Further, the following processes may be included, if desired.Specifically, after the process (2), (3) a process of rinsing theengraved surface with water or a liquid mainly consisting of water, (4)a process of drying the engraved relief-forming layer and (5) a processof further crosslinking the relief-forming layer may be performed.

The process (1a) or (1b) is a process of crosslinking the relief-forminglayer of the resin printing plate precursor for laser engraving. Therelief-forming layer according to the invention preferably includes thebinder polymer, the light-to-heat conversion agent (D), thepolymerization initiator (E) and the polymerizable compound (C), and theprocess (la) or (lb) is a process of polymerizing the polymerizablecompound (C) by the action of the polymerization initiator (E) to formcrosslinkage. The polymerization initiator (E) is a radical initiatorand roughly classified into a photopolymerization initiator and a heatpolymerization initiator depending on whether the trigger for generatinga radical is light or heat.

In the case where the relief-forming layer contains aphotopolymerization initiator, the relief-forming layer is irradiatedwith an active ray which is a trigger of the initiation ofphotopolymerization so that the relief-forming layer can be crosslinked.The irradiation of active ray is ordinarily performed on the all oversurface of the relief-forming layer. As the active ray, visible light,an ultraviolet ray or an electron beam is exemplified and theultraviolet ray is most ordinarily used. Assuming that a surface of therelief-forming layer facing to the support is a back surface, it isenough to irradiate only the surface of the relief-forming layer, butwhen the support is a transparent film which transmits the active ray,it is preferred to further irradiate the relief-forming layer with theactive ray from the back surface. In the case where a protective film ispresent, the irradiation from the surface may be performed through theprotective film or may be performed after removing the protective film.Since the polymerization inhibition may occur in the presence of oxygen,the irradiation of active ray may be performed after covering thecrosslinkable relief-forming layer with a vinyl chloride sheet andvacuuming.

In the case where the relief-forming layer contains a heatpolymerization initiator (the photopolymerization initiator describedabove may also be the heat polymerization initiator), the relief-forminglayer can be crosslinked by heating the resin printing plate precursorfor laser engraving. As the heating means, a method of heating theprinting plate precursor in a hot air oven or a far-infrared oven for aprescribed time or a method of bringing the printing plate precursorinto contact with a heated roll for a prescribed time is exemplified.

According to the process (1a) using light, since the printing plateprecursor is not subjected to high temperature, there is littlerestriction on raw materials for the printing plate precursor, althoughan apparatus for irradiating the active ray is relatively expensive.Although the process (1b) using heat is advantageous in that thespecific expensive apparatus is not needed, it is necessary to carefullyselect the raw materials used for the printing plate because theprinting plate precursor is subjected to high temperature and there is apossibility that a thermoplastic polymer which becomes soft at hightemperature is deformed during the heating.

In the case of the heat crosslinkage, a heat polymerization initiatormay be added. In principle, as the polymerization initiator, acommercial heat polymerization initiator for free radicalpolymerization, for example, an appropriate peroxide, a hydroperoxide ora compound having an azo group is used. Representative vulcanizingagents are also used for the crosslinkage.

The heat crosslinkage is also performed by adding a heat-curable resin,for example, an epoxy resin as the crosslinking component to the layer.

As the crosslinking method of the relief-forming layer of the resinprinting plate precursor for laser engraving, the crosslinkage byheating is more preferable according to the invention from thestandpoint that the relief-forming layer can be cured (crosslinked)uniformly from the surface to the inside. According to thephoto-crosslinkage, a problem in that the light is preferentiallyabsorbed in the surface of the relief-forming layer so that the lightcan not sufficiently reach to the deep portion of the relief-forminglayer may occur sometimes whereby the difficulty in that the degree ofcuring (crosslinkage) is uneven between the surface and inside of therelief-forming layer may arise (in case of the heat crosslinkage, asufficient amount of heat is uniformly applied from the surface to theinside of the relief-forming layer).

By crosslinking the relief-forming layer, advantages are obtainedfirstly in that the relief formed after the laser engraving becomessharp and secondly in that tackiness of engraved scrap occurred at thelaser engraving is restrained. When a non-crosslinked relief-forminglayer is engraved with laser, due to residual heat transmitted aroundthe laser irradiation area a portion which is essentially not intendedto be engraved is apt to melt or deform so that a sharp relief can notbe obtained in some cases. Also, as a general property of material, asdecreasing a molecular weight of the material, it tends to change from asolid to a liquid form, specifically, to increase tackiness. Theengraved scrap occurred at the laser engraving of the relief-forminglayer has a tendency toward increase in the tackiness as increasing theamount of materials having a low molecular weight used. Since thepolymerizable compound (C) having a low molecular weight becomes a highmolecular compound by the crosslinkage, the engraved scrap occurredtends to decrease the tackiness.

It is preferred that a shore A hardness of the relief-forming layerafter the crosslinkage is from 50 to 90°. By using the relief-forminglayer having the shore A hardness of 50° or more, the minute halftonedots formed by the engraving are not collapsed even when a strongprinting pressure of a letterpress is applied to them so that normalprinting can be performed. By using the relief-forming layer having theshore A hardness of 90° or less, the occurrence of thin spots in thesolid image area can be prevented even in a flexographic printing inwhich a kiss touch printing pressure is used.

The process of laser engraving the crosslinked relief-forming layer (2)is a process in which the relief-forming layer is irradiated with alaser beam corresponding to the image to be formed to form a reliefimage. The process is preferably performed by controlling a laser headbased on digital data of the image to be formed using a computer andirradiating the relief-forming layer with scanning. When an infraredlaser is irradiated, molecular vibration of the molecule in therelief-forming layer occurs to generate heat. When a high output laser,for example, a carbon dioxide gas laser or a YAG laser is used as theinfrared laser, a large amount of heat is generated at the laserirradiated area and the molecule in the relief-forming layer undergoesmolecular scission or is ionized to be selectively removed, that is, toperform engraving. The advantage of the laser engraving is that thestructure can be three-dimensionally controlled because the depth ofengraving can be appropriately set. For instance, in the area whereminute halftone dots are printed, the halftone dots are shallowlyengraved or engraved to form shoulders so that collapse of the reliefdue to the printing pressure can be prevented. The channel for printinga fine outline character is deeply engraved so that printing ink canhardly fill the channel and collapse of the fine outline character canbe prevented.

In particular, when the engraving is performed using an infrared lasercorresponding to the maximum absorption wavelength of the light-to-heatconversion agent (D), a sharper relief image is obtained at highersensitivity.

When the engraved scrap is attached on the engraved surface, the processof rinsing the engraved surface with water or a liquid mainly consistingof water (3) to wash away the engraved scrap may be introduced. As therising means, for example, a method of spraying high-pressure water or amethod of rubbing the engraved surface with a brush in the presence ofwater as the main component using a batch type or transporting typebrush washing out machine known as a developing machine for aphotosensitive resin anastatic printing plate is exemplified. When thetackiness due to the engraved scrap is not removed, a rinsing solutionincluding soap may be used.

When the process of rinsing the engraved surface (3) is conducted, it ispreferred to introduce the process of drying the engraved relief-forminglayer (4) to volatilize the rinsing solution.

Further, if desired, the process of further crosslinking therelief-forming layer (5) may be performed. By performing the additionalcrosslinking process (5), the relief formed by the engraving is morestrengthened.

The relief printing plate produced according the method of the inventionallows printing by a letterpress with oil-based ion or UV ink and alsoallows printing by a flexographic printing machine with UV ink.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples, but the invention should not be construed asbeing limited thereto.

Example 1

In a three-necked flask equipped with a stirring blade and a condenserwere put 50 g of poly(DL-lactide) (produced by Aldrich Corp.) as thepolyester (A), 0.75 g of D99-009 (phthalocyanine compound, produced byYamamoto Chemicals Inc.) as the light-to-heat conversion agent (D), 20 gof diethylene glycol as the plasticizer (F) and 50 g of n-butanone asthe solvent and the mixture was heated at 65° C. for 120 minutes withstirring to dissolve the polymer. To the solution were further added 28g of DPHA (dipentaerythritol hexaacrylate, produced by Toagosei Co.,Ltd.) which was an ethylenically unsaturated monomer as thepolymerizable compound (C) and 1.6 g of Irgacure 184 (a-hydroxyketone,produced by Ciba-Geigy Corp.) as the polymerization initiator (E) andthe mixture was stirred for 30 minutes to obtain a fluent solution ofcrosslinkable resin composition for laser engraving for use in acrosslinkable relief-forming layer.

A spacer (frame) having a prescribed thickness was put on a PETsubstrate, the solution of resin composition for laser engraving wassoftly cast in the spacer (frame) not to overflow and dried in an ovenof 70° C. for 3 hours to form a relief-forming layer having a thicknessof about 1 mm, whereby a resin printing plate precursor for laserengraving was prepared.

Then, the relief-forming layer of the resin printing plate precursor washeated at 100° C. for 2.5 hours to perform heat crosslinkage of therelief-forming layer.

FD-100 equipped with a semiconductor laser having the maximum output of16 W (laser emission wavelength of 840 nm) (produced by ToseiElectrobeam Co., Ltd.) was used as an infrared laser engravingapparatus. Under the engraving conditions of laser output of 15 W, scanrate of 100 mm/sec and pitch distance of 0.15 mm, a solid image area of2 centimeters square was engraved to prepare a relief printing plate.

The depth of engraving was determined by observing the cross-section ofthe solid image area by Ultra-deep Color 3D Profile Measuring MicroscopeVK9510 (produced by Keyence Corp.) and measuring a difference of heightbetween the surface of relief-forming layer and the engraved portion.The results obtained are shown in Table 1 together with the results ofevaluations described below.

Examples 2 to 4

The same procedures were performed as in Example 1 except for changingthe poly(DL-lactide) to poly(3-hydroxybutyrare) for Example 2,poly(ε-caprolactone) for Example 3 and poly(butylenesuccinate) forExample 4, respectively.

The number average molecular weight of the poly(DL-lactide),poly(3-hydroxybutyrare), poly(ε-caprolactone) andpoly(butylenesuccinate) used in Examples 1 to 4 was 90,000, 30,000,20,000 and 60,000 respectively.

Example 5

In a three-necked flask equipped with a stirring blade and a condenserwere put 10 g of Landy PL-2000 (polylactic acid, produced by Miyoshi Oiland Fat Co., Ltd.) as the polyester (A), 40 g of Gosenal T-215 (PVAderivative, produced by Nippon Synthetic Chemical Industry Co., Ltd.) asthe binder (B), 0.75 g of Ketjenblack EC600JD (carbon black, produced byLion Corp.) as the light-to-heat conversion agent (D), 20 g ofdiethylene glycol as the plasticizer (F) and 35 g of water and 12 g ofethanol as the solvents and the mixture was heated at 70° C. for 120minutes with stirring to dissolve the polymer. To the solution werefurther added 28 g of DPHA (dipentaerythritol hexaacrylate, produced byToagosei Co., Ltd.) which was an ethylenically unsaturated monomer asthe polymerizable compound (C) and 1.6 g of Irgacure 184(α-hydroxyketone, produced by Ciba-Geigy Corp.) as the polymerizationinitiator (E) and the mixture was stirred for 30 minutes to obtain afluent solution of crosslinkable resin composition for laser engravingfor use in a crosslinkable relief-forming layer.

The same procedures was performed as in Example 1 except for using theabode-described solution of crosslinkable resin composition for laserengraving in place of the solution of crosslinkable resin compositionfor laser engraving of Example 1.

Example 6

The same procedures were performed as in Example 5 except for changingthe DPHA to the compound shown below.

Example 7

The same procedures were performed as in Example 6 except for changingthe carbon black to equivalent amount of ADS820HO (cyanine compound,produced by American Dye Source, Inc.).

Example 8

The same procedures were performed as in Example 6 except for changingthe carbon black to equivalent amount of D99-009 (phthalocyaninecompound, produced by Yamamoto Chemicals Inc.).

Example 9

The same procedures were performed as in Example 6 except for furtheradded 5 g of aquaPASS-01X (conductive polyaniline, produced byMitsubishi Rayon Co., Ltd.).

Example 10

The same procedures were performed as in Example 6 except for furtheradded 5 g of Panipol-W ((conductive polyaniline, produced by PanipolLtd.).

The shore A hardness (23° C.) of the relief-forming layer after the heatcrosslinkage in Examples 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 was 75°, 60°,70°, 80°, 77°, 70°, 68°, 69°, 81° and 73°, respectively.

Examples 11 to 20

The same procedures were performed as in Examples 1 to 10 except forchanging the laser for engraving from the semiconductor laser to a CO₂laser described below, respectively.

CO₂ Laser Marker ML-Z9500 equipped with a carbon dioxide gas laserhaving the maximum output of 30 W (produced by Keyence Corp.) was usedas a carbon dioxide gas laser engraving apparatus. Under the engravingconditions of laser output of 15 W, scan rate of 100 mm/sec and pitchdistance of 0.15 mm, a solid image area of 2 centimeters square wasengraved to prepare a relief printing plate.

Comparative Example 1

The same procedures were performed as in Example 6 except that the LandyPL-2000 was eliminated and the PVA derivative was compensated therefor.

Comparative Example 2

The same procedures were performed as in Example 6 except for changingthe total amount of Landy PL-2000 and the PVA derivative to equivalentamount of TR-2000 (styrene-butadiene rubber, produced by JSR Corp.).

Comparative Examples 3 to 4

The same procedures were performed as in Comparative Examples 1 to 2except for changing the laser for engraving from the semiconductor laserto the CO₂ laser described above, respectively.

Depth of Laser Engraving Engraving (μm) Example 1 Semiconductor Laser560 Example 2 ″ 510 Example 3 ″ 520 Example 4 ″ 520 Example 5 ″ 520Example 6 ″ 600 Example 7 ″ 600 Example 8 ″ 600 Example 9 ″ 650 Example10 ″ 650 Example 11 CO₂ Laser 365 Example 12 ″ 330 Example 13 ″ 330Example 14 ″ 330 Example 15 ″ 330 Example 16 ″ 390 Example 17 ″ 390Example 18 ″ 390 Example 19 ″ 420 Example 20 ″ 420 Comparative Example 1Semiconductor Laser 460 Comparative Example 2 ″ 400 Comparative Example3 CO₂ Laser 280 Comparative Example 4 ″ 250

From the result shown in Table 1, it can be confirmed that by theaddition of the polyester (A), the depth of engraving is larger and theengraving sensitivity is higher in comparison with the case wherein thepolyester (A) is not added.

1. A resin composition for laser engraving comprising a binder polymercomprising at least one polyester (A) selected from the group consistingof a polyester comprising a hydroxycarboxylic acid unit,polycaprolactone, poly(butylene succinic acid), and derivatives thereof.2. The resin composition for laser engraving as claimed in claim 1,wherein the polyester (A) is selected from the group consisting of apolyhydroxyalkanoate, a lactic acid polymer, polyglycolic acid,polycaprolactone, poly(butylene succinic acid), and derivatives thereof,and mixtures thereof.
 3. The resin composition for laser engraving asclaimed in claim 1, wherein the polyester (A) is selected from the groupconsisting of a polyhydroxyalkanoate, a lactic acid polymer,polyglycolic acid, and derivatives thereof, and mixtures thereof.
 4. Theresin composition for laser engraving as claimed in claim 1, wherein thebinder polymer further comprises a hydrophilic polymer.
 5. The resincomposition for laser engraving as claimed in claim 4, wherein thehydrophilic polymer is a polyvinyl alcohol derivative.
 6. The resincomposition for laser engraving as claimed in claim 1, which furthercomprises (C) a polymerizable compound.
 7. The resin composition forlaser engraving as claimed in claim 1, which further comprises (D) alight-to-heat conversion agent capable of absorbing light having awavelength of from 700 to 1,300 nm.
 8. The resin composition for laserengraving as claimed in claim 7, wherein the light-to-heat conversionagent (D) is selected from the group consisting of carbon black, acyanine compound and a phthalocyanine compound.
 9. A resin printingplate precursor for laser engraving comprising a relief-forming layercomprising the resin composition for laser engraving as claimed inclaim
 1. 10. A method for production of a relief printing platecomprising: (1) a process of crosslinking the relief-forming layer asclaimed in claim 9 with at least one of light and heat; and (2) aprocess of laser engraving the crosslinked relief-forming layer.
 11. Themethod for production of a relief printing plate as claimed in claim 10,wherein the process (1) is a process of crosslinking the relief-forminglayer with heat.
 12. A relief printing plate produced by the method asclaimed in claim
 10. 13. The relief printing plate as claimed in claim12, wherein a thickness of the relief-forming layer crosslinked is 0.05mm or more.
 14. The relief printing plate as claimed in claim 12,wherein a shore A hardness of the relief-forming layer crosslinked isfrom 50 to 90°.